Pidgin is a universal Instant Messaging client capable of using AIM/ICQ, Yahoo!, GTalk, MSN, IRC, Jabber, Napster, Zephyr, Gadu-Gadu, Bonjour, Groupwise, Sametime, SILC, and SIMPLE all at once. Formerly known as the 'GAIM Messenger' for Linux.
Kopete is an instant messenger program which can communicate with a variety of IM systems, such as Yahoo, ICQ, MSN, IRC and Jabber. Kopete includes the "Now Listening" plug-in that can report what music you are currently listening to, in a number of different players, including xmms, noatun, kscd, juk, kaffeine and amarok.
Konversation is a client for the Internet Relay Chat (IRC) protocol. It is easy to use and well-suited for novice IRC users, but novice and experienced users alike will appreciate its many additional features including multiple server and channel tabs, multiple identities, smart-logging, and more.
XChat-GNOME is not a fork of XChat, rather it simply uses a more friendly front-end for the X-Chat IRC client and is designed for people who care more about chatting than tweaking personal settings in their client.