A multi-protocol instant messaging app for Mac OS X
Adium is an Open Source, multi-protocol instant messaging application for Mac OS X. Adium supports AIM, ICQ, Jabber, MSN, Yahoo!, Google Talk, Bonjour, Gadu-Gadu, Novell Groupwise, SIP/SIMPLE (Text), and Lotus Sametime. Additionally, it supports all of these applications at once so, even if you have multiple IM accounts, you don't have to log into each account separately.
pork, oidentd, iplog and ocd
Fire is a multi-protocol instant messenger client for Mac OS X based on freely available libraries for each service. Currently Fire handles AOL Instant Messenger®, ICQ®, MSN® Messenger, Jabber, limited IRC, Yahoo!®, and Apple Bonjour communications.
BIM is a Java based AOL Instant Messenger (AIM) Client featuring a full feature Swing GUI. BIM also comes with encryption support. It has a small code base (617KB w/encryption libs) and can be easily dropped and run on wide array of operating systems.
The PlanetaMessenger.org Libraries project is a set of open source instant messenger libraries used and maintained by PlanetaMessenger.org. You can find protocol implementation for MSN, ICQ, ComVC networks for use on standalone and server applications.
Proteus is a multi service instant messaging application for Mac OSX. At the core of Proteus is this Service Controller! This controller provides a common interface for any number of applications to plug into. Each application that knows how to commun
TikiTwit is an Open Source, GPL'ed Cocoa application that automatically synchronizes iChat and twitter.com status messages.