Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more. Adium is written using Mac OS X’s 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.
Requirements: Mac OS X 10.4 or newer
Download: Adium 1.3.10
License: GNU GPL