It allows users to communicate instantly through text to their "buddies" around the world, provided they have the AIM software. AIM has 195 million users (January 2003), with a large proportion using Internet slang. Advocates claim that it's easy to locate these users by visiting chatrooms that AOL has set up solely for those purposes. Chat topics range from *NSYNC to current affairs. AOL also has a member directory where AIM users can locate others online who share their interests.
Since version 2.0, AIM has included person-to-person text messaging, chatroom messaging, and the ability to share files peer-to-peer with your buddies. Unlike Napster, and other peer-to-peer software, there is no directory of files, only direct person-to-person transfer of files, protecting AOL from intellectual property lawsuits. Somewhere in the 4.x series, the AIM client for Microsoft Windows added the ability to play games against one another. Recent (4.3 and later) versions of the client software store your contact information on AOL's servers, so you can talk to up to 200 of your buddies from any computer with Internet access. Stand-alone official AIM client software is available for free for Microsoft Windows, Mac OS, Linux, Windows CE, and Palm OS. However, some users stay on the 3.0 series because the software license agreement for 4.0 and later clients includes a clause prohibiting the user from ever using a third-party client program.
There is also a client called AIM Express implemented as an applet for the Java platform that runs in your web browser. AIM Express does not have all the features of stand-alone AIM clients, such as file transfer or buddy icons (although you can view others'), but it still allows the basic functions of person-to-person text messaging.
The standard protocol that AIM clients use to communicate is called OSCAR. AIM Express uses another protocol called TOC. TOC has also been made available to the public, in an attempt to throw a bone to third-party client developers and lure them away from OSCAR. This scheme has not been entirely successful. AOL has continually changed the details of the OSCAR protocol to keep third-party clients such as Trillian from working properly. This has resulted in a cat-and-mouse game between AOL and the client developers.
Apple Computer's iChat AV software for Mac OS X was the first AIM-compatible client to allow for audio and video conferencing over the AIM protocol. It was released in June, 2003. In February, 2004, AIM 5.5 was released, allowing Windows users to video conference with each other and with Mac iChat users. Unfortunately, AIM 5.5 did not allow audio-only chats as iChat AV does.
AIM software is the first to use online video streaming advertisements, via the Eyewonder protocol.