Pidgin

Google Talk and sitting in a Yahoo chat room all at the same time. Pidgin runs on Windows Linux and other UNIX operating systems. Pidgin is compatible with the following chat networks out of the box AIM ICQ Google Talk Jabber/XMPP MSN Messenge Yahoo Bonjour Gadu-Gadu IRC Novell GroupWise Messenger QQ Lotus Sametime SILC SIMPLE MySpaceIM and Zephyr. It can support many more with plugins.