Free Web Meeting Environments?

doval asks: "I just took a look at Webex and Centranow. For those of you who have seen these sites, is there an open source equivalent? For those of you who have not, they offer the following (currently wintel only): Presentation Sharing, Document Sharing, Application Sharing, Web Co-browsing, File Transfer, Desktop Sharing, Telephony Integration, Internet Voice, and Video Integration. Think MS Meeting, ICQ, PC-to-phone, and PC-to-PC all in a browser (synchronous). I am familiar with open source bits and pieces like OpenH323, Jabber, plus collaboration environments like Zope. However, I do not know of anything like the sites I mentioned. Particularly, I would like to get my hands on a good example of Web synchronous application sharing and PC-to-phone."