BitlBee allows users to talk to people on the major instant messaging and microblogging networks (including MSN, Google Talk, AIM, and Twitter) from within any IRC client by emulating an IRC server. Virtual channels are created with all of the user's contacts in them, who can be talked to in the channel or in a query. Also, one can participate in group chats and chat rooms like they were normal IRC channels.
Pidgin is a GTK2-based instant messenger application. It supports multiple protocols via modules, including AIM, ICQ, Yahoo!, MSN, Jabber, IRC, Napster, Gadu-Gadu and Zephyr. It has many common features found in other clients, as well as many unique features. Pidgin is not endorsed by or affiliated with AOL TimeWarner, Microsoft, or Yahoo.
Licq includes all the basic features of ICQ, like sending/receiving messages, chat, file transfer, contact list with pixmaps and user status, basic/extended user info, adding/editing users from within the GUI, user history, user groups, and new user registration. All commands and information are available through a simple and convenient tab dialog. Licq also has a completely configurable user interface with Skin and Icon pack support. It is written in C++ and comes with a GUI plugin using the Qt widget set. Other plugins are also available, like basic MSN support.
JClaim is an instant message client, tools, and development framework. It supports AIM, ICQ, Yahoo!, MSN, Jabber, Google Talk, and SMS. The framework can be used for designing your own tools. The UI includes spell checking and a lot more. A Web interface is included for remote access.
YSM (You Sick Me) v7 is an ICQ console client. It was originally meant to run in Linux, but it has been successfully tested in Linux, BSD, Win32, BeOS, and QNX. The client requires no extra libraries, and is written in the C language. YSM is based on the last ICQ protocol version, v7/8.
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.