Adium is a free and open source instant messaging application for Mac OS X, written using Mac OS Xs Cocoa API, released under the GNU GPL and developed by the Adium team. Based on the libpurple protocol library, Adium can connect you to any number of messaging accounts on any combination of supported messaging services and then chat with other people using those services.
Dead for years...
I must say, I am very impressed with Adium. It is a very capable IM client. It support almost everything!
I agree with sceptiQ :-D
Adium is a must-have for Mac users, especially if you have multiple IM accounts for different protocols.
And I love some of the themes and emoticon sets…