A list of Java instant messaging client libraries. Not intended to be exhaustive, just some I've come across while Googling.

AIM

• Joust -- low level OSCAR api
• jaimlib -- supports TOC protocol
• jaimbot -- Java AIM bot, includes a library
• SimpleAIM -- console AIM client

MSN

• JMSN -- MSN messenger clone, not actually a library, but there's likely to be stuff to reuse
• MSNj -- another MSN library, looks quite old
• jmml

Yahoo

??

Jabber

• Smack
• jabberc
• ...and probably a million more...