TerraIM (Popularity: )
http://terraim.sourceforge.net/ TerraIM is a free, light, stylish AOL Instant Messenger. Requires no install and fits on a floppy.
Y!TunnelPro (Popularity: )
http://www.ytunnelpro.com/ Add-on aiming to protect Messenger users from abusive and malicious chatroom activity. [Requires Windows].
Yahoo Messenger (Popularity: )
http://messenger.yahoo.com/ Allows you to instant message with anyone on the Yahoo server. Tells you when you get mail, and gives stock ...