Kopete - Kopete is an instant messenger supporting AIM, ICQ, MSN, Yahoo, Jabber, IRC, Gadu-Gadu, Novell...
Gajim - Full featured and easy to use Jabber client
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.
CoyIM - CoyIM is a safe and secure chat client.
Facebook Messenger - Facebook Messenger is a faster way to message.
Empathy - Apps/Empathy - GNOME Wiki!