ChatKit
ChatKit is now officialy dead
See this post for more info.
ChatKit, is a project designed to give developers all tools needed to build a complete functional IM client from the ground up.
It consists of two sections: a framework+daemon and utilities. The utilities section contains general stuff that are not directly connected to IM clients, but may be useful to them like tabs, update system, pretty controls, and so on.
ChatKit v0.5 offers the base classes for working with all IM networks although only Apple’s Bonjour is supported at this time.
Version 0.5 can send/receive messages, send/receive status and status messages, send/receive typing status notifications, send/receive contact images and support both plain text messages and HTML messages.
v0.5 is also fully bindings compatible, and introduced a new CKMessage class that takes care of all the info related to messages, and encodes/decodes HTML messages to/from NSAttributedString.
Just to give you a general idea about ChatKit, we implemented full client in about ~250 lines of actual code (only!!). The code of that client is included in the distribution and provides a demonstration of using the ChatKit API.
The two major utilities hosted by the ChatKit project are Sparkle and PSMTabBarControl and they share the same subversion repository and trac with ChatKit.
The ChatKit project is located at www.chatkit.net.
The latest release is available from http://www.chatkit.net/wiki/Downloads