Gabber is a Jabber client for GNOME. Jabber is a flexible distributed Open Source instant messaging system. It also happens to allow communication with other instant messaging systems, such as ICQ, AIM, Yahoo!, MSN, and even IRC. Gabber aims to implement quite a bit of Jabber's functionality while remaining easy to use.
Kopete is a flexible and extendable multiple protocol instant messaging system designed as a plugin-based system. All protocols are plugins and allow modular installation, configuration, and usage without the main application knowing anything about the plugin being loaded. The goal of Kopete is to provide users with a standard and easy to use interface between all of their instant messaging systems, but at the same time also providing developers with the ease of writing plugins to support a new protocol. The core Kopete development team provides a handful of plugins that most users can use, in addition to templates for new developers to base a plugin on.
Kit is an AIM client for KDE. It has a standard KDE UI, has standard KDE sound and other notification support, and uses the open protocol for reliable service. It has shipped with many operating systems, and so undergone many hours of testing and portability work. It also integrates with KDE session management and system tray features.