Pidgin

Pidgin (formerly named Gaim) is an open-source multi-platform instant messaging client. Initial release: 1998 as Gaim.

Pidgin is a chat program which lets you log in to accounts on multiple chat networks simultaneously. This means that you can be chatting with friends on MSN, talking to a friend on Google Talk, and sitting in a Yahoo chat room all at the same time.

Pidgin is compatible with the following chat networks out of the box: AIM, ICQ, Google Talk, Jabber/XMPP, MSN Messenger, Yahoo!, Bonjour, Gadu-Gadu, IRC, Novell GroupWise Messenger, Lotus Sametime, SILC, SIMPLE, MXit, MySpaceIM, and Zephyr. It can support many more with plugins.

Pidgin supports many features of these chat networks, such as file transfers, away messages, buddy icons, custom smilies, and typing notifications. Numerous plugins also extend Pidgin's functionality above and beyond the standard features.

Pidgin features some of the standard tools for an instant-messaging client, such as a contact list, file transfer on supported protocols, and conversation and chat logging. Tabbed conversations is an optional feature on Pidgin. The IM window consists of the message window, formatting tools, and an edit box.

Users can add contacts (usually known as "Buddies") in the "Buddy List" window or in the IM window. As a client that supports IRC and other chat programs, Pidgin can also add different IRC channels and IM Chats. Contacts with multiple protocols can be grouped into one single contact instead of managing multiple protocols, and contacts can be given aliases or placed into groups.
Further features include support for themes, emoticons, spell checking, and notification area integration.