Miranda IM is an open source, multi-protocol instantmessaging client designed to be very light on system resources, extremely fast and customizable. A powerful plugin-based architecture make Miranda IM one of the most flexible clients on the planet.
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.
Ayttm is an instant messenger program, supporting various protocols such as MSN, Yahoo, AIM, Jabber, and more. It is the heir of the Everybuddy project, and aims to continue improving the program and addressing its shortcomings.
Fire is a multi-protocol instant messenger client for Mac OS X based on freely available libraries for each service. Currently Fire handles AOL Instant Messenger®, ICQ®, MSN® Messenger, Jabber, limited IRC, Yahoo!®, and Apple Bonjour communications.
The BeOS Instant Messaging Kit project aims to create a BeOS-centric, generic instant messaging servuice for workstations. The system will follow the BeOS kits/servers model, and different IM protocols will be supported through add-ons to the im_server,