Gaim does it all. Just like many GNOME/GTK programs, it lacks some of the design and feature bells and whistles of its KDE counterpart, but it makes innovations in function. The Gaim developers have regular releases and are among the most responsive when it comes to fixing reported bugs. Having a parallel Windows version means that you can keep the same program and interface even if you have to use Windows for some reason. Also, the program is self-contained and can run equally well in KDE and GNOME.
Kopete
Good
Great
Kopete started off slow but has caught up to Gaim in most respects, while adding a few twists of its own. If you are a regular user of the KDE desktop, the integrated features Kopete uses with KAddressBook, the system tray, and KNotify will be great.
Yahoo! Messenger
Good
Fair/poor
You won't ever have to worry about not being able to connect to Yahoo!'s changing protocols when you are using their client, but you won't have as many features, either. It's admirable that Yahoo! has cared enough to make a Linux version of their IM program, but it would be nice if they kept it up-to-date. Not only does the interface look old compared to other Linux programs, but it doesn't even keep up with the features that Yahoo!'s client for Windows has. This one is good to keep on hand as a backup.
ChatZilla
Fair
Fair
ChatZilla is a fairly new program that Mozilla lists as not finished yet. The program is one of those that works just fine but has no fun toys in it to play with. The fact that you can launch it right from your browser is convenient.
Xchat
Good
Good
XChat is made only for IRC chat, and that's what it does well. The built-in server list and well-planned menu choices make this the most straightforward and easy IRC client to use.
