ShadowIRC is a fast IRC client for the Mac OS. The program is extensible with C-coded plug-ins compiled with CodeWarrior. This makes ShadowIRC plug-ins faster and more flexible than AppleScript-based scripts, though you will need knowledge of C and a copy of CodeWarrior if you are going to write plug-ins. Among other features, ShadowIRC can process Ircle and mIRC color codes (though not at the same time). The source code
is also available.