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

Trillian is a proprietary multiprotocol instant messaging application.

Miranda NG is a successor of Miranda IM, a popular multi-protocol instant messaging client for Windows.

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

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

Gajim is an instant messaging client for the XMPP protocol which uses the GTK+ toolkit.

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