Pidgin is a free and open-source chat client which supports AIM, Google Talk, ICQ, XMPP protocols.

Tox is a peer-to-peer instant-messaging and video-calling protocol that offers end-to-end encryption.

Kopete is a multi-protocol, free software instant messaging client released as part of the KDE Software Compilation. Although it can run in numerous environme…

iMessage is an instant messaging service.

Adium is an Open source multi-protocol instant messaging client for Mac OS X, supports MSN, Jabber, Yahoo! and other networks.

Trillian is a proprietary multiprotocol instant messaging application.

Instantbird is a cross-platform instant messaging client based on Mozillas XULRunner and the open source library libpurple used in Pidgin.

Tkabber is a GPL instant messaging client for the XMPP protocol which uses the Tk toolkit for the GUI.