As usual, this thread has wandered pretty far from the original topic, which is a shame considering that this is a fairly important issue for a lot of people. I do actually have a little experience in this area, so here's what I know that might help:
wxWindows: If you're going to stick to a C++ cross-platform application framework, I honestly believe this is the best option. Most people don't seem to pay much attention to it, and many of those who have were burned by bugs in earlier versions, but it's really starting to come together in terms of both stability and functionality. I ported early code for a pretty complex program from MFC to wxWindows within 2 months, which impressed me considering that I wasn't familiar with either toolkit and that was my first real use of C++. I'm now doing a bit of work with wxPython, which is also going pretty well. The Mac port development tends to lag a bit behind the others, but it has been (and is being) used to deliver several commercial products, so it seems to be in usable condition; I haven't had a chance to test it myself yet. By all means, please carefully consider this option; it seems to be the most capable framework of it's type currently out there, has a respectable number of users and developers, and will get even better with more support.
CPLAT: Afraid I can't say anything as positive about this one; the MFC project I mentioned above was itself a port from CPLAT. After 2 months of development with CPLAT (ending January 2000), the developers unanimously agreed that the framework was so buggy that it would be faster to write separate versions of the program for MFC and PowerPlant. I believe there is only one developer on the project; that simply isn't enough resources to properly handle a framework of this magnitude.
Whisper: We looked at this one also, but it didn't have enough of the features we were looking for to be worth trying. It also looked to be, like CPLAT, a one-man effort.
YAAF: Another one we passed over after a brief glance. The web site didn't have much information, and I don't see any indication that it's being used much. I may have short-changed it, but I just don't see enough activity around it to indicate a really good product.
GLUI: I haven't used this or looked too closely at it yet. The lack of native widgets bothers me, though...
Carbonless Copies: Hadn't heard of this before. The web site given above hasn't been updated in a while, I haven't heard of many people using it, and it's a proprietary program; I'd be inclined to avoid it.
Regarding some of the other options people have suggested:
Java: While useful for some purposes, cross-platform GUIs arguably isn't one of them. It's relatively easy to get a Java GUI program to work cross-platform, but practically impossible to get it to work well. AWT lacks major functionality. Swing is buggy and a *massive* memory hog; don't even think about running Swing apps on computers with 32 MB of RAM, and they're not terribly happy even with 64 MB. And Java in general is lagging far behind on the Mac. Finally, it is a proprietary platform complete with all of the problems that entails. I used to really like Java, but not much progress has been made at solving some of it's critical deficiencies. I'm now hoping Python can take it's place...
Mozilla: Mozilla is useful, but it's deficiencies have been noted above; lack of native widgets, slow response time to user input, etc. I look forward to using this for some projects, but it isn't going to replace the need for a cross-platform C++ application framework.
GTK+: Doesn't work on the Mac, and won't for some time to come. Doesn't use native widgets on Windows, either (to my admittedly limited knowledge.) I agree with the wxWindows approach; use GTK+ on Windows, use the Windows API on Windows, and use the MacOS API on the Mac.
Qt: Again, doesn't work on the Mac and doesn't use native widgets on Windows.
Tk: Doesn't have native look and feel, and last I checked has some issues on MacOS. I've also gotten the impression that the widget selection isn't as rich as that of wxWindows, although I haven't looked at it closely enough to judge for myself.
On the topic of RAD tools; wxWindows does not yet have a usable RAD tool, although the wxStudio IDE is under development and there is a working dialog and panel editor. wxPython has the Boa Constructor IDE which seems to be almost in usable condition; it could also be argued that compared to using C++, even manually writing Python code practically *is* a RAD environment.
Hope this successfully addresses some of the issues, and hope it isn't buried so far down in the responses that it never gets noticed...
Slashdot Mirror
As usual, this thread has wandered pretty far from the original topic, which is a shame considering that this is a fairly important issue for a lot of people. I do actually have a little experience in this area, so here's what I know that might help:
wxWindows: If you're going to stick to a C++ cross-platform application framework, I honestly believe this is the best option. Most people don't seem to pay much attention to it, and many of those who have were burned by bugs in earlier versions, but it's really starting to come together in terms of both stability and functionality. I ported early code for a pretty complex program from MFC to wxWindows within 2 months, which impressed me considering that I wasn't familiar with either toolkit and that was my first real use of C++. I'm now doing a bit of work with wxPython, which is also going pretty well. The Mac port development tends to lag a bit behind the others, but it has been (and is being) used to deliver several commercial products, so it seems to be in usable condition; I haven't had a chance to test it myself yet. By all means, please carefully consider this option; it seems to be the most capable framework of it's type currently out there, has a respectable number of users and developers, and will get even better with more support.
CPLAT: Afraid I can't say anything as positive about this one; the MFC project I mentioned above was itself a port from CPLAT. After 2 months of development with CPLAT (ending January 2000), the developers unanimously agreed that the framework was so buggy that it would be faster to write separate versions of the program for MFC and PowerPlant. I believe there is only one developer on the project; that simply isn't enough resources to properly handle a framework of this magnitude.
Whisper: We looked at this one also, but it didn't have enough of the features we were looking for to be worth trying. It also looked to be, like CPLAT, a one-man effort.
YAAF: Another one we passed over after a brief glance. The web site didn't have much information, and I don't see any indication that it's being used much. I may have short-changed it, but I just don't see enough activity around it to indicate a really good product.
GLUI: I haven't used this or looked too closely at it yet. The lack of native widgets bothers me, though...
Carbonless Copies: Hadn't heard of this before. The web site given above hasn't been updated in a while, I haven't heard of many people using it, and it's a proprietary program; I'd be inclined to avoid it.
Regarding some of the other options people have suggested:
Java: While useful for some purposes, cross-platform GUIs arguably isn't one of them. It's relatively easy to get a Java GUI program to work cross-platform, but practically impossible to get it to work well. AWT lacks major functionality. Swing is buggy and a *massive* memory hog; don't even think about running Swing apps on computers with 32 MB of RAM, and they're not terribly happy even with 64 MB. And Java in general is lagging far behind on the Mac. Finally, it is a proprietary platform complete with all of the problems that entails. I used to really like Java, but not much progress has been made at solving some of it's critical deficiencies. I'm now hoping Python can take it's place...
Mozilla: Mozilla is useful, but it's deficiencies have been noted above; lack of native widgets, slow response time to user input, etc. I look forward to using this for some projects, but it isn't going to replace the need for a cross-platform C++ application framework.
GTK+: Doesn't work on the Mac, and won't for some time to come. Doesn't use native widgets on Windows, either (to my admittedly limited knowledge.) I agree with the wxWindows approach; use GTK+ on Windows, use the Windows API on Windows, and use the MacOS API on the Mac.
Qt: Again, doesn't work on the Mac and doesn't use native widgets on Windows.
Tk: Doesn't have native look and feel, and last I checked has some issues on MacOS. I've also gotten the impression that the widget selection isn't as rich as that of wxWindows, although I haven't looked at it closely enough to judge for myself.
On the topic of RAD tools; wxWindows does not yet have a usable RAD tool, although the wxStudio IDE is under development and there is a working dialog and panel editor. wxPython has the Boa Constructor IDE which seems to be almost in usable condition; it could also be argued that compared to using C++, even manually writing Python code practically *is* a RAD environment.
Hope this successfully addresses some of the issues, and hope it isn't buried so far down in the responses that it never gets noticed...