Gaim is a multi-protocol instant messaging client for Linux, BSD, MacOS X, and Windows. It is compatible with AIM (Oscar and TOC protocols), ICQ, MSN Messenger, Yahoo, IRC, Jabber, Gadu-Gadu, and Zephyr networks.
Gaim users can log in to multiple accounts on multiple IM networks simultaneously. This means that you can be chatting with friends on AOL Instant Messenger, talking to a friend on Yahoo Messenger, and sitting in an IRC channel all at the same time.