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

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

ICQ is an open source instant messaging software.

WhatsApp Messenger is an instant messaging platform owned by Facebook.

Trillian is a proprietary multiprotocol instant messaging application.