AOL Instant Messenger (AIM)
AIM, otherwise known as AOL Instant Messenger is a freeware instant messaging program that uses the OSCAR instant messaging protocol and the TOC protocol. It is ad-supported and was released by AOL in early 1997.
Since AIM reached version 2.0 in 1999 it has had the ability to person to person text messaging, chatroom messaging and the ability to send files between peers. Newer version allow for "invisibility" modes, the option to save 600 of your friends as contacts, and the ability to play games and see the weather.
AIM is available on all platforms and can be accessed through IM clients such as Trillian, Miranda IM, iChat and Gaim.
The newest version available of AIM, as of March 2007, is AIM 6.0, formerly known as AIM Triton.