...It is written in C and makes heavy use of GLib and GTK+.
Finch is a command line instantmessaging program. It also lets you log in to accounts on multiple chat network simultaneously, and it is compatible with the same chat networks as Pidgin. It is written in C and makes heavy use of GLib and ncurses.
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.
It is an instantmessaging client. Crony IM has support for some commonly used instantmessaging protocols, allowing the user to log into various different services from one application. like LAN, GTalk, Yahoo, Facebook.
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.
Provides an overlay notification of events while using Gaim InstantMessaging client. This software utilizes the xosd library and should therefore support any platform that xosd and Gaim support.