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.

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

Facebook Messenger is the official Facebook app that lets you have text conversations with all of your friends on the popular social network.

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

ICQ is an open source instant messaging software.

iMessage is an instant messaging service.

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…

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.

Fring connects with Skype, MSN Messenger, ICQ and Google Talk from your iPhone.

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