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

Coccinella is a free and open-source cross-platform client for the XMPP/Jabber-instant messaging-protocol.

Dialog Messenger is a handy and feature-rich enterprise multi-device messenger available for server or cloud.

Disa is your new messaging hub. Conversations from different services can seamlessly be joined together, or disbanded within seconds.

Finch is a console-based IM program that lets you sign on to AIM, Jabber, MSN, Yahoo!, and other IM networks. It runs on Unixes. It uses GLib and ncurses.

ICQ is an open source instant messaging software.

Bit Chat is a secure, peer-to-peer, open source instant messenger with end-to-end encryption.

Conversations is an open source XMPP/Jabber client for the Android platform.

Digsby provides you with IM, email and Social networks in one easy to use application.

Empathy is an instant messaging (IM) and voice over IP (VoIP) client which supports text, voice, video, file transfers, and inter-application communication ov…

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

IM+ supports simultaneously major IM services, including Google Talk, Twitter DMs, Yahoo!, AIM/iChat, ICQ, Jabber (and Slack through Jabber), etc.