AIM (AOL Instant Messenger) is an instant messaging program that uses the OSCAR instant messaging protocol and the TOC protocol to allow registered users to communicate in real time. It was released by AOL in May of 1997.
Yahoo! Messenger is another popular instant messaging program provided by Yahoo!. It is used with a generic "Yahoo! ID" which also allows access to other Yahoo! services, and chat rooms in various categories. it was released on 21 June 1999. It is the first major IM client to feature BUZZing and music-status. Another recently added feature is customized avatars.
Comparison chart
 | AOL Instant Messenger | Yahoo Messenger |
|---|---|---|
| Author/Creator | America Online | Yahoo! Inc |
| Latest version available | 6.5.9.1 (Windows) 2.4,1.0.2 Build 110 Beta (Pro (Win),1.3.30.1 (Triton (Win),4.7.1333 (Mac OS X),1.5.286 (Linux | 8.1.0.244 (Win),2.5.3 (Mac),1.0.4 (Unix) |
| Operating systems supported | Windows, Windows mobile, Blackberry smartphones | Windows, Blackberry |
| Operating systems not supported | Mac X, Mac OS X, Linux, BDS ,Unix | Mac X, Mac OS X, Linux, BSD, Unix, Windows Mobile |
| Encryption | Yes | No |
| Protocols | AIM and ICQ | Windows Live messenger, Yahoo! messenger, Lotus SameTime |
| Toolkits or SDKs | W32 | W32, Cocoa, GTK |
| Built-in games | Partial | Yes |
| File transfer | Yes | Yes |
| Unicode (UTF-8) | Yes | Yes |
| Voice messaging and Mail | Yes | Yes |
| Web cam Support | Yes | Yes |
| Offline messaging | Yes | Yes |
| Message Logging | Yes | Yes |
| Themes / skins | Yes | Yes |
| Emoticons | Yes | Yes |
| Cost | Free | Free |
| Licence | Clickwrap licence | Clickwrap licence |
| Remote desktop application assistance | No | No |
| Whiteboard | No | Yes (Doodle) |
| Third party add-ons | Yes | No |
| Plugin system | Yes | Yes |
| Multi-account support | No | Yes (with Microsoft Live IDs) |
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Comments: AOL Instant Messenger vs Yahoo Messenger