AIM for Linux
- An AOL instant messaging application. Latest stable release is 1.5, 2003-01-10. N.B.: This software uses a modification of the GTK Library (available at http://www.gtk.org) and is licensed under LGPL.
Centericq
- A console-based instant messaging system which supports the ICQ2000, Yahoo!, AIM, IRC and Jabber protocols.
Citadel
- An open source groupware platform which includes email, calendaring & scheduling, address books, bulletin boards, mailing list server, instant messaging, and multiple domain support.
Coccinella
- A cross-platform Jabber client. Key features include an integrated whiteboard, P2P file transfer, multilingual support, group chat, secured connections (TLS and SASL), and an open standard instant messaging protocol (can connect to any Jabber/XMPP instant messaging server). Coccinella is the Latin name for ladybug.
Jabber Software Foundation
- Open XML protocol for an asynchronous, extensible instant messaging platform, and an IM network.
Kopete
- A KDE instant messenger; a flexible and extensible multi-protocol system suitable for personal and enterprise use.
Licq Homepage
- An ICQ/AIM clone written in C++. It uses an extensive plugin system to manage many different functions including the MSN protocol. Latest release is 1.3.6, 2008-10-02.
Off-the-Record Messaging
- This instant messaging application allows private conversations by providing encryption, authentication, deniability, and perfect forward secrecy (if private keys are compromised, no previous conversation is compromised)
Pidgin- IM Client
- A cross-platform, multi-protocol instant messaging (IM) client for GNOME; multilingual support. Formerly called Gaim.
Psi Jabber Client
- A cross-platform, open source instant messaging software built on the Jabber protocol.
SIM
- An open source ICQ client. Latest release is 0.9.4.3, 2007-04-04.