Yahoo! Messenger is a popular instant messaging client and protocol provided by Yahoo!. Yahoo! Messenger is provided free of charge and can be downloaded and used with a generic "Yahoo! ID" which also allows access to other Yahoo! services, such as Yahoo! Mail, where users can be automatically notified when they receive new email. Yahoo! offers PC to PC telephone, file transfers, webcam hosting, text messaging service, and chat rooms in various categories. In addition to instant messaging features similar to those offered by ICQ, it also offers (on Microsoft Windows) many unique features such as: IMVironments (customizing the look of Instant Message windows), address-book integration and Custom Status Messages. It was also the first major IM client to feature BUZZing and music-status. Another recently added feature is customized avatars.

Features:

* Yahoo! Voice - Yahoo! Voice is a Voice over IP PC-PC, PC-Phone and Phone-to-PC service provided by Yahoo! via its Yahoo! Messenger instant messaging application.
* Voicemail and file sharing - Yahoo! added voicemail and file sending capabilities to their client. File-sharing of sizes up to 1GB was added.
* Plug-ins -As of 8.0, Yahoo! Messenger has added the ability for users tocreateplug-ins (via the use of the freely available Yahoo! MessengerPlug-inSDK), which are then hosted and showcased on the Yahoo!Plug-ingallery.
* Interoperability with Windows Live Messenger-This allows, for Yahoo! and Windows Live Messenger users to chattoeachother without the need to create an account on theotherservice,provided both contacts use the latest versions of theclients. For now,it's impossible to talk using the voice service amongbothmessengers.