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

Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application.

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…

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

qutIM is free and open-source multiprotocol (ICQ, Jabber, Mail.Ru, IRC, VKontakte) instant messenger.

AIM is a instat messenger application.

YakYak is a desktop chat client for Google Hangouts.

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

Psi is a free instant messaging application designed for the XMPP network (including Google Talk). Fast and lightweight, Psi is fully open-source and compatib…

Franz is a free messaging app /former emperor of Austria, that combines chat & messaging services into one application.

Smuxi is a cross-platform IRC client for the GNOME desktop inspired by Irssi.

QuteCom (WengoPhone) is a free-software SIP-compliant VoIP client.

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