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Email is dead!!!
If someone want to compete with Exchange have to invent something else, something like "buletinboard" with Calendar and Tasks...

It's already been invented

Here's two: Citadel and Kolab

Among other things, Kolab is a product of a series of contracts for the federal office for Security in the Information Technology in the German Government, though both are quite secure.

Then there are two more: OpenGroupware and Zimbra. Module options are out there. If you're not finding them, then it's because you are not looking.

I've used Citadel. It is not a bad groupware package. It is open source, easy to install, and actively maintained. I don't believe it supports encryption of the database and it uses a file attachment model rather than a file server model. However, it works fairly well for calenders and messaging.

In a word ... Citadel. (Disclaimer: I am a developer on this project, and yes, I'm flogging it here.) Contacts, calendars, notes, documents, email, etc etc. One single installation without a zillion dependencies.

Having spent considerable time developing calendar software I can tell you that time zone handling is the ugliest part of the picture. It certainly would be best if everything, everywhere, was on UTC.

For a while, we simply converted everything to UTC on the way in to the system, and all was good. We simply converted back to local time when interacting with the user. But then we had to add support for recurring events. This was a bitch and a half because of DST being observed in some parts of the world, and not being observed in other parts of the world. If you converted a recurring event to UTC, the recurrences would be an hour off the next time you entered or exited DST. Really a pain in the neck, and it required storing all recurring events in local time.

Sadly, most people don't write and maintain calendar software, and are quite attached to their local time. So much so, in fact, that they can't even comprehend doing it any other way.

Every time groupware/Exchange related topics appear on Slashdot (often as not an "open" replacement solution that isn't quite open, or not quite there, or both), I see a couple of references to the Citadel project:

http://www.citadel.org/

This appears to be a very interesting offering, and I've never understood why it doesn't generate more buzz. Can anyone knowledgeable in this subject explain what is lacking in Citadel to make it a serious contender in this domain? It is compatibility with Outlook/Exchange, missing features, not scalable, or ...?

http://citadel.org/ Citadel uses a proper database back-end and can handle terabytes of mail for thousands of users.

Lots of comments here debating the relative merits of Twitter and Facebook, but the original poster was asking for alternatives.

I say, go out and find yourself a good old fashioned BBS, make friends there, invite friends there, and have fun. One possibility is this nice little place which has been online for 22 years and has a great friendly bunch of people.

What a great machine. The Altos 586 was the first machine I used to run my BBS (which has run nonstop since 1988 and is still online today) before SCO Xenix and later Linux arrived on the scene. It was an insanely cool computer.

Anyway, even if there were an operating system available today that is still capable of parsing the Xenix filesystem, you wouldn't be able to get to it because the disk is attached to the system I/O board using an ST506 controller. Good luck finding a modern computer with one of those in it.

You're going to have to move that data off the machine the way we did it back in the days when an Altos was a modern computer. Plug a null modem cable into that serial port and use UUCP to get the data moved. Or if the machine has rzsz installed, you might be able to get away with using Zmodem instead.

it's the first time I've felt the simplicity and friendliness on an Internet forum that good old BBSes had back in the 80s.

You might also enjoy Citadel, which started life as a BBS package and is now popular as a groupware platform. People are still using it to run online communities, too.

Guaranteed? I suppose you don't admin any MTAs and don't know what you are talking about.

Not only do I admin a large number of MTA's, but I've also written one. I know how SMTP works.

You definitely want to try out the Citadel groupware server. Even if you don't need it for its mail system, address book, calendar, etc... it's got a built in XMPP (Jabber) service that integrates nicely across the entire environment. It also logs all of the instant messages sent through it. Each user can review their own logs too, which is nice. And you have the ability to journal everything that comes through the system, perhaps to an external archiving service (this feature was built with industries like yours in mind, where anything that gets read by anyone *must* be archived).

And it's free software ... GPL 3, to be exact.

I can't believe there hasn't been any mention of Berkeley DB yet. Guess what, folks: sometimes you just don't need the features of a full relational database. Sometimes all you need is fast, robust, reliable storage of indexed key/value pairs.

I can attest that Berkeley DB does exactly that, and does it really, really well. We use Berkeley DB for all of the data storage in the Citadel system, including the mailboxes themselves. Some sites have tens of gigabytes or even hundreds of gigabytes of data, and Berkeley DB just keeps chugging along, happily and reliably doing its thing. Our biggest problem? People who point at it and say "storing email in a database is unreliable" because they know it constantly explodes when Exchange does it. Well guess what, folks: Berkeley DB ain't the Exchange database (actually, maybe Exchange wouldn't be so unreliable if they switched to Berkeley DB).

Eschewing the full set of RDBMS features isn't slacking. It's choosing the right tool for the job.

There really aren't very many more "killer apps" to be invented. This is completely opinion, but I think SharePoint is going to be Microsoft's last hurrah. It is their last chance to get organizations tied into a single, unified respository for all of their content. SharePoint is like a Wiki on steroids, but it doesn't necessarily need to be a proprietary Microsoft technology. They have the benefit of being able to easily integrate their Office Suite with SharePoint. As a proprietary vendor, they have the benefit of being able to issue edicts to their developers and align a lot of resources toward a common goal. Accomplishing the same thing in OSS land would take a lot of coordination and would probably require an outfit like IBM or the like to develop a competing project.

Competing OSS products already abound.

Alfresco is probably the pick of them.

http://www.alfresco.com/

Does everything that Sharepoint does, but does it for free, with no CALs, and so that you can run Windows, Mac or Linux as desktop clients. OpenOffice has extensions for using it with Alfresco.

Linux application support is getting better every day. Just take a look at Zimbra. Now, I'm not about to scrap MY Exchange servers and migrate my users to Zimbra. But if I were a small business owner and I needed email for my company, I wouldn't even be looking at the cost of Exchange licenses.

OpenChange also is on its way.

http://www.openchange.org/

There is also Citadel to consider.

http://www.citadel.org/doku.php

Samba 4 will support Active Directory and, of course, be a capable file server.

http://www.computerworld.com.au/article/273515/active_directory_comes_linux_samba_4

All free (no cost) and Free (freedom) as well. All of these OSS solutions will support Windows, Mac or Linux desktop clients, or any mixture of them. There is absolutely no need to pay any more for server software or server access licenses.

Enjoy. Prosper.

For an SMB with no history, there are many more options available for you than for older businesses which need to support legacy stuff.

The Google Apps method mentioned by bplipschitz is $50 per user per year, and will offer much of the functionality at a low cost with a limited SLA and no maintenance. If I were starting a new business right now, I'd probably try to make this one work and create a work-flow around it while backing up data locally on a regular basis. Once Google comes out with an Apps version of the Google Mini, it should be a go-to choice for a lot of businesses. Right now, though, the whole system's pretty new and that worries some folks. Don't believe the "Google Beta" FUDders -- the Premium Edition has an SLA and isn't marked "beta" (but it also doesn't have the newest features in the Free "beta" version).

eGroupware is an extremely mature web-server based collab suite with Echange functions plus project management, a wiki a DMS (more limited than Sharepoint), and a knowledge base. The whole thing can use LDAP for auth, meaning that it can tie into an AD or LDAP-Kerberos setup. It uses IMAP and ICAL protocols for client software if you want that. It's free, but you need to admin your own hardware. There are support contracts available.

There's also Citadel, which has been pushed really hard lately in a lot of Open Source press, but which I've never used. People say it's able to work with Outlook directly, is mature, and is feature-complete. It's free, but there doesn't appear to be official paid support on the site.

If you're willing to go the Google Apps method, you should also look into Zoho. It's also $50 per user per year, but the first ten are free. If I had a bunch of users used to MS Office, I think Zoho would be an easier transition to hosted for them than Google Apps would be. I like GA better for its simplicity, though. Zoho is more integrated and pollished, but it doesn't have the real-time collaboratiion.

I had a conversation with one of the openchange developers a few months ago to talk about some of the architecture being built here, and was pleased to find out that they're aiming to do something useful. They do want OpenChange to be useful as a standalone server. That gets you something Outlook can talk to. But they're also going to expose all of the right API's and stuff so that OpenChange can be integrated with an existing store or server. That means that with the right amount of glue code, we'll be able to integrate it with existing open source groupware servers like Citadel or Kolab or OpenGroupware. All of these servers currently have Outlook compatibility, but you need to add a plugin to Outlook in order to make it work. With any luck, OpenChange will allow Outlook to talk to all of these excellent FOSS groupware platforms as if they were Exchange servers.

(Not that I'm knocking the plugins, mind you ... some of them are excellent. I'm particularly fond of Bynari's connector which is totally seamless, works with open source groupware servers, and costs far less than Exchange licenses. But a connector-free option will be nice too.)

Can you give examples of good Exchange replacements?

Yes, for that see DVL. Seriously, though you have to define what activities you need to do before you can ask for a replacement. MS Exchange is marketed in many niches and fails (on the surface) in most. The most spectacular is its failure as a mail server replacement, if you look at it as such. If you look at the wonderful cover of plausible deniability it gives executives by randomly losing and delaying mail, then that is a success.

Anyway, try looking these. Keep in mind that, unlike with M$ products, you can combine pieces of several packages.

• Kolab — http://www.kolab.org/
• Citadel — http://www.citadel.org/
• Dingo Calendar Server — http://andrew.triumf.ca/dingo/
• Darwin CalendarServer — http://trac.calendarserver.org/
• Bedework — http://www.bedework.org/
• Zimbra — http://www.zimbra.com/
• OpenGroupware — http://www.opengroupware.org/

If you are simply looking to improve reliability of e-mail they a plain Mail Transfer Agent (MTA) will do. Before it became too embarrassing for M$, it used to be recommended practice to put one of these in front of MS Exchange to improve reliability and security. Also look up ClamAV, Spamassassin and how to do greylisting.

• simta — http://rsug.itd.umich.edu/software/simta/
• Dovecot — http://www.dovecot.org/
• Postfix — http://www.postfix.org/
• Exim — http://www.exim.org/
• Sendmail — http://www.sendmail.org/
• qmail — http://www.qmail.org/

However, before you can think about "replacing" MS Exchange, you will have to get rid of the staff that selected and deployed it in the first place. They ignored all the licensing shortcomings, the bad reviews, high price and ongoing technical failure to instead push ideology over technology. People making decisions based on ideology are not going to accept any technical or economic arguments...

Can you give examples of good Exchange replacements?

Yes, for that see DVL. Seriously, though you have to define what activities you need to do before you can ask for a replacement. MS Exchange is marketed in many niches and fails (on the surface) in most. The most spectacular is its failure as a mail server replacement, if you look at it as such. If you look at the wonderful cover of plausible deniability it gives executives by randomly losing and delaying mail, then that is a success.

Anyway, try looking these. Keep in mind that, unlike with M$ products, you can combine pieces of several packages.

• Kolab — http://www.kolab.org/
• Citadel — http://www.citadel.org/
• Dingo Calendar Server — http://andrew.triumf.ca/dingo/
• Darwin CalendarServer — http://trac.calendarserver.org/
• Bedework — http://www.bedework.org/
• Zimbra — http://www.zimbra.com/
• OpenGroupware — http://www.opengroupware.org/

If you are simply looking to improve reliability of e-mail they a plain Mail Transfer Agent (MTA) will do. Before it became too embarrassing for M$, it used to be recommended practice to put one of these in front of MS Exchange to improve reliability and security. Also look up ClamAV, Spamassassin and how to do greylisting.

• simta — http://rsug.itd.umich.edu/software/simta/
• Dovecot — http://www.dovecot.org/
• Postfix — http://www.postfix.org/
• Exim — http://www.exim.org/
• Sendmail — http://www.sendmail.org/
• qmail — http://www.qmail.org/

However, before you can think about "replacing" MS Exchange, you will have to get rid of the staff that selected and deployed it in the first place. They ignored all the licensing shortcomings, the bad reviews, high price and ongoing technical failure to instead push ideology over technology. People making decisions based on ideology are not going to accept any technical or economic arguments...

Exchange and SharePoint are huge money-suckers. There are plenty of open source alternatives, such as Citadel and Kolab and OpenGroupware. Give them a try and get that migration started.

Having implemented OpenID 1.1 Relying Party support myself, I think I can definitely see what Google is up to, and it isn't evil, people. OpenID 1.1 was elegant simplicity. Our team built OpenID Relying Party support in just a couple of days without even using any external libraries. OpenID 2.0, on the other hand, is a disaster. Its architecture reeks of design-by-committee. There were four different groups vying to define the standard for single-sign-on for the web, so what did they do? They basically just glommed all of the different technologies together and called it OpenID 2.0. There are all sorts of things you have to support, like I-Names (which no one is going to use). In the end our team decided to just implement OpenID 1.1 and rely on the recommendation for backward compatibility which is built into OpenID 2.0 (a recommendation which Yahoo ignored, btw).

So it's very possible that some engineers at Google said "hold on a minute. This sucks. OpenID 1.1 made a lot more sense, let's build out from there and see if it's something that the Internet community accepts."

It may even come to pass that both OpenID 2.0 and Goopen-ID both end up specifying backwards compatibility to OpenID 1.1, which would be great because it would effectively halt the progress of the over-engineered OpenID 2.0 and put us back on a saner path.

Let's not call Google's plans evil until we see where this goes. It could end up being something that finally puts this useful technology into some widespread use.

They already do. I've done support for W.A. schools that were having problems with their internal Exchange server. They were shocked when we discussed the 'real' price for Exchange. They paid less than $1000 for it including CALs and hardware. MS has some serious sweetheart deals for schools and I bet if it came down to providing even cheaper Windows and Office for schools they will do it.

That's not the real price, though. The real price also includes all the down time, extra re-builds, malware tools, etc. Add to that also the cost of missing incoming messages, missing outgoing messages and delayed messages -- these last add up to more work for the users, which can number in the 100's, rather than just the maintenance staff which can usually be counted on one hand.

Before MS Exchange was hammered through the back door, e-mail was both so fast and reliable that many used it in ways resembling instant messaging.

Worth a look:
Roundcube: http://roundcube.net/
Kolab: http://www.kolab.org/
Citadel: http://www.citadel.org/
Zimbra: http://www.zimbra.com/

If you need a plain vanilla mail transfer agent instead of all the non-essentials, then postfix, exim, qmail, the new sendmail, and simta each have their niche. They're used pretty much everywhere, even if you don't always see the evidence of them outside the message headers.

Hmm, for a few bucks month you can run your own mail server. Citadel http://www.citadel.org/ installs in about 20 minutes and is zero maintenance. There is no easier email system on the planet and it Just Works (TM).

That's a nice long explanatory answer... for the first question! ;). Do you have an answer for the 2nd?

I might even add... do you have suggestions?

I have already checked out a few of 'em (not necessarily OSS):

• Zimbra
• Scalix
• eGroupware
• PHP Groupware
• Communigate Pro
• Citadel
• Kolab
• Open Groupware
• Open xChange

...of which many of them have a great potential, but I always end up having some trouble somewhere or find 'em not user-friendly/admin-friendly enough.

Citadel also tries to be a full-featured e-mail/calendaring/task management/etc system.

(Yes, deliberately provocative subject. Please read on.)

UseNet originated at a time when a vast portion of its network was built upon store-and-forward technologies such as UUCP, BITNET, and various homegrown protocols for the smaller sites. If you could do store and forward you could probably carry newsgroups.

Today, everyone has interactive Internet access. That's why no one is scrambling to "fix" UseNet. Today's users Google for what interests them, and they eventually find themselves on a relevant message board. That message board is probably not replicated to thousands of other servers across the globe, because the whole world can already reach it directly.

The only nuisance is that you have to create accounts on all these systems. Hopefully, technologies such as OpenID will fix that.

(And yeah, there are plenty of smaller message boards that thrive specifically because they are smaller scale than UseNet. I've been a BBS sysop for 20 years, and our community is thriving because everyone has the opportunity to know everyone else without having to deal with a 1% signal to noise ratio. It also helps that we offer both text and web based user interfaces to the same message boards, so we can be equally as welcoming to newbies and old-skool green screeners.)

It's time the free software world merged PIM with social networking.

Disclaimer: this is something that I originally wrote on a BBS. So it's appropriate but not an "original for today."

The BBS never really died. Thats a myth perpetrated by Slashdot (if ever there were a central repository for groupthink, Slashdot is it) as well as self-proclaimed pundits in the tech trade rags who are always waxing eloquent about the "next big thing." Sure – the Internet did change the world, and it continues to do so. But when it comes to people interacting with each other online, that process began when Ward Christensen and Randy Suess put their first system online in 1978, and it has continued uninterrupted since then. It moved from dialup to the Internet.

Today, various developers are finding new and innovative ways to optimize their messaging platforms for different audiences. For example, millions of American teenagers are now BBS users: they are all subscribed to a large BBS called MySpace. Responses to this assertion which begin with the words "But MySpace isnt a BBS, its a" will be summarily ignored because they indicate that you havent given more than ten seconds of thought to the subject. Forums, chat, email doesnt all of this sound more than a little bit familiar? Even the "BBSs are from yesteryear" groupthink over at Slashdot is particularly ironic, considering that Slashdot itself is basically just a big BBS optimized for the reporting and discussion of tech news.

You can call it a BBS, or you can call it groupware, or you can call it "social software" (the new favorite buzzword for the tech marketing dweebs). Call it whatever you want but its basically the same thing. Messaging is messaging. Its just a question of how you optimize it for your audience.

The fact is, I really haven't run into an organization that DOESN'T want Windows+Exchange. As far s I can tell, it's only the cost that drives anyone away.

Where is the BlackBerry plugin?

Where is the IM plugin?

Where are the anti-virus plugins?

Where is the document collaboration?

How do I use a real database? Where are the automated backup tools?

How do I cluster Citadel?

Which Winows desktop clients work absolutely perfectly with Citadel?

and most importantly, Where can I hire a consultant that will do all this for me?

What mail protocols do you offer other than POP3 and IMAP? Let's assume for the moment that you rip out these protocols... what exactly can you do with the Citadel system now? I know you have the web client, but does that use HTTP to transfer mail?

You kind of left out a party in your "win-win" analysis. How about customers? I have one very real group of customers in mind--Zimbra customers.
What are the odds Microsoft would have allowed it to flourish? I'm betting that, at a minimum, they would have jacked the price up until it was no longer as cost effective over Exchange.

Pardon me, but I have to mention Citadel http://citadel.org./ This system is easy to install, zero maintenance, and with BerkeleyDB as the back-end, it scales pretty well. Citadel is a very good system for small to medium size businesses and will probably be able to handle large businesses as well.

Zimbra and Scalix don't count as true FOSS because they are scaled-down crippleware. If you want the full feature set of either one, you have to pay. Insert RMS rant here (this is one of those situations where it's relevant). These two companies went with a (just barely) open source license for two reasons: (1) cheap street cred, and (2) so they could help themselves to existing code without paying for it or developing it in-house.

There is plenty of good messaging/collaboration software out there that is true FOSS and not some bastardized commercial hybrid. Citadel and Kolab come to mind as a few of the most versatile.

The idea that messaging/collaboration is a gap in the Linux stack is a complete myth. There are numerous options available, such as Citadel which is end-to-end GPL code, has all of the most requested groupware functions, and even has an Outlook connector available for those PHB's who aren't ready to leave the old world behind yet. I wish people would stop pushing this idea that Outlook/Exchange can't be matched.

Our employees are hooked on Outlook, journals especially (I loathe them, space
eating buggers) so we keep exchange chugging along and a couple of domain
controllers.

Our employees are hooked on Outlook, journals especially (I loathe them, space eating buggers) so we keep exchange chugging along and a couple of domain controllers.

It's more than a case of killing the goose that lays the golden eggs. Gatesists made clear that they would not take "no" for an answer and would continue their plans against Yahoo one way or another. These so-called pension funds are likely part of that approach and just softening up Yahoo, while setting the media against the board in prep for its ousting. One point which is unlikely to ever make many mainstream news sites or forums, even open source ones like Slashdot, is that Microsoftologians are likely to try to replace Yahoo's board. Poisoning the press against the board is a first step.

Later, preventing the Yahoo employees from jumping off with golden parachutes might be a repeat of what MS did to Borland, except against key open source projects. Yahoo contributes in a big way to many open source projects, PHP and BSD being two Very Important (tm) ones. Getting Yahoo would crush a competitor to the spectacularly failed MSN. So without the 'chutes many would have to stay and MS could simply have them sweeping floors or making coffee.

There is also the question of Zimbra, which was recently purchased by Yahoo. MS Exchange is about the only thing that ties Windows into either/both the desktop and the server room. Zimbra is one of the few competitors to MS Exchange, besides Kolab and Citadel, none of which get much press. Quite a few shops would stop or drastically decrease use of MS products without MS Exchange. Zimbra is currently not GPL. Buying Yahoo would allow Zimbra to be put on ice as MS did with FoxPro

Advertising, aka tracking users, is another problem. MS execs want into advertising. Controlling the adservers allows a chance, finally, at income. It also allows access to be tweaked. Ads get served up first before content and delay, especially at the beginning, drastically reduces viewing time and thus mindshare. The first moments are crucial and studies show that the cap is set at 20s. A delay, on purpose or by accident, of even a fifth of a second x one million page views is hundreds of lost viewing hours. So the potential for severe abuse is there in addition to the technical problems MS services and servers are known for.

At the bottom is also a question of money. Many articles somehow neglect that much of the initial offer was funny-money, aka MSFT stock, which MS prints on demand. The noise and smoke about the attempted take over does well at drawing attention away from what must be some rather 'creative' book keeping there in Redmond.

There are plenty more possible reasons to go after Yahoo's board. Having sockpuppets poison the press makes sense for many of them.

You might want to try Citadel, which has integrated email, group conversations and shared calendaring.

My recollection is that Zimbra has some very funky goings-ons in their licensing, and I'm not sure if "Freedom to Fork" is preserved in a reasonable way. (A license that forces derivatives to show their trademarked logo?) Therefore, I have never considered deploying Zimbra on the principle that in event of Zimbra's failure that a knowledge-vacuum would cause other firms to pick up the product.

Plus many of the modules that makes Zimbra actually useful are closed source.

For now I'd rather deploy Citadel ( http://www.citadel.org/ ) w/GroupDAV ( http://www.groupdav.org/ ). In particular its speed, turnkey-style administration, and replication options (thanks to BerkeleyDB) make it pretty attractive on the whole.

For more information, see
http://www.rants.org/2007/06/26/when-is-open-source-not-open-source/

The OSS version of Zimbra is just that, Open Source. Whatever happens there should be no change in that status.

Don't forget they also own Zimbra, an OSS Outlook/Exchange competitor

furasato - I was just noticing your feature request. Might I suggest logging into bugzilla and entering a feature request? http://bugzilla.citadel.org/. This way it won't get lost in the chatter online here. It would be great if you ran out of excuses not to use Citadel. -Aahz

Software that actually works. It's in use. It's actively being maintained. As new technology is released, there's a proven track record of it being incorporated into the software.

Then you're really making a mistake if you don't look at citadel.

Email, Calendaring, Contacts, multiple interfaces, multiple standards compliant protocols, instant messaging and it all can run on one server. But wait.. It scales! So if you want to run multiple servers and have them communicate, go ahead. It's built right in.

Visit http://citadel.org/ for more information and to download or there's even a vmware appliance, all set up and ready to go. All you need to do is download and run. Try http://www.vmware.com/appliances/directory/723. -

If you want a calendar and e-mail solution, you might want to take a peek at Citadel.

Yes, it has a web interface, but you do not have to use it (just as Exchange). It offers IMAP, POP3, and SMTP protocols for working with mail. Currently, a company named Bynari even has an Outlook plugin that works with it, although I do not know how well.

You'll need to install it on a Unix-like machine rather than Windows. You can decide for yourself if that's good or bad.

But, maintenance is significantly easier than Exchange, and it offers calendaring in a standards-compliant way.

If you want, you can try it out for yourself (although outbound e-mail is necessarily disabled because spammers would otherwise abuse it) at Uncensored, where you can also ask support-related questions.

It has a very long history, and a pretty stable pedigree. The developers also try to be as responsive as possible... and it's open-sourced. Of course.

Some folks think of it as one of the internet's best kept secrets. Give it a spin and decide for yourself.

If you want a calendar and e-mail solution, you might want to take a peek at Citadel.

Yes, it has a web interface, but you do not have to use it (just as Exchange). It offers IMAP, POP3, and SMTP protocols for working with mail. Currently, a company named Bynari even has an Outlook plugin that works with it, although I do not know how well.

You'll need to install it on a Unix-like machine rather than Windows. You can decide for yourself if that's good or bad.

But, maintenance is significantly easier than Exchange, and it offers calendaring in a standards-compliant way.

If you want, you can try it out for yourself (although outbound e-mail is necessarily disabled because spammers would otherwise abuse it) at Uncensored, where you can also ask support-related questions.

It has a very long history, and a pretty stable pedigree. The developers also try to be as responsive as possible... and it's open-sourced. Of course.

Some folks think of it as one of the internet's best kept secrets. Give it a spin and decide for yourself.

You really want to check out Citadel. It has a very comprehensive feature set -- not just calendars but also email, address books, message boards, instant messaging, access via all standard protocols plus a gorgeous ajax-style web user interface.

The best part about Citadel is that it is very easy to install. There's an automatic installer script right on the web site. No fuss, no muss, just enter the install command and watch it go. No tedious mucking about with integrating all of the pieces yourself, as the entire Citadel system is self-contained.

And the whole thing is GPL, unlike solutions such as Zimbra and Scalix which claim to be open source, but when you actually go there you find out that to get the full feature set you have to buy a commercial version. The Citadel project makes its very best work available to everyone on the same terms.

Citadel is the best kept secret on the internet. Installs in no time and does everything: http://www.citadel.org/

Take a look at Citadel. It does Groupdav, Kolab1, and a few others as well. Calendar, Contacts, and Email. And it's 100% GPL.

Citadel is the best i know of: http://www.citadel.org/doku.php

how about: http://www.zimbra.com/ http://www.citadel.org/

All newer Microsoft clients are aiming to switch from this original RPC driven protocol to WebDAV through OWA.