A fork of pidgin which aims to provide minor features that have not been addressed by the pidgin development team (including manual textbox resizing). See funpidgin.sf.net for details.
An useful foundation class package.
Jiim is a Web-based Instant Messaging system that overcomes the language barrier, letting you read and type in your mother tongue.
PlanetaMessenger.org is a Instant Messenger with support to all well known instant messenger networks including ICQ,MSN,AIM,Yahoo! and Jabber through a powerfull plugin engine. PlanetaMessenger.org support multiples look and feels, plugins and profiles.