JTelIRC is an advanced IRC framework for Java. It is mainly intended for writing automated clients ("bots"), but may be used for normal clients as well. It provides an intuitive and well documented Java interface to IRC and makes it extremely easy to write advanced clients quickly.
JAIMBot is a modular architecture for providing services through an AIM client. It contains a generic AIM library and a Bot which uses this library to provide such services as Offline Messaging, Lists, Weather, Headlines, Stock Quotes, TV Listings, and an AI chatterbot. You can try out this project with a live AIM bot called JavaAIMBot. Send it "help" as an instant message to see what it can to.
Echomine Feridian is an easy-to-use Java API that gives you quick and easy access to the XMPP network used in IM services such as Google Talk. The API allows you to communicate with Jabber/XMPP servers for sending and receiving instant messages, presence management, and custom extensions to the XMPP protocol.
The JabberWookie Library for Jabber is intended to be a complete, extensible, simple-to-use Java implementation of the Jabber protocol (a.k.a. XMPP). It makes heavy use of the SSTTR XML Library as well as the SSTTR Crypto and Utility Libraries. The SSTTR Libraries are the only non-core Java libraries on which it is dependent.
daim is an IM client and library that supports many features, including add-ins, AIM proxy, buddy icons, chat, direct IM, file transfer, file sharing, send buddy list, and Trillian secureIM. It also supports retrieving News and Stocks, and scripting through Apache BSF. It also supports ICQ, can emulate Apple's iChat client, and supports iChat available messages as well.