Ircle - Internet Relay Chat for the Mac (English or French). - http://www.ircle.com/
ChitChat - Open Source RealBASIC Yahoo chat client for Mac OS 9 and X. - http://chit.sourceforge.net/
Fire - A multi-protocol IM client for OS X; supports the six most popular instant messaging services as well as IRC chatting. - http://fire.sourceforge.net/