Pidgin - Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...
Miranda IM - Miranda IM is the smaller, faster, easier instant messenger with support for multiple protocols.
Empathy - Apps/Empathy - GNOME Wiki!
Gajim - Full featured and easy to use Jabber client
Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.