Yahoo! Messenger, a popular instant messaging client provided by Yahoo! You need a Yahoo! ID which also allows access to other Yahoo! Services such as Yahoo! Mail.

Features.

Yahoo! Messenger automatically notified users they receive new emails. It also offers PC-PC, PC-Phone and Phone-PC service, file transfers, webcam hosting, text messaging service, and chat rooms in many categories.
Yahoo! Messenger also offer another features such as: IMVinvonments, address-book integration integration and Custom Status Messages.
Now Windows Live Messenger  is compatible with Yahoo! Network.

Yahoo! Voice: Yahoo! Voice is a Voice over IP PC to PC, PC to Phone and Phone to PC service, provided by Yahoo! via its Yahoo! Messenger instant messaging application.
Voicemail and file sharing: Is a voicemail and file sending service provided by Yahoo!  File-sharing of sizes up to 1GB.
Plug-ins: Yahoo! Messenger allow users to create plug-ins (via the use of the freely available Yahoo! Messenger Plug-in SDK), which are then hosted and showcased on the Yahoo! Plug-in gallery.
Yahoo! Mail integration: As Yahoo! Mail Beta and Yahoo! Messenger have been integrated, conversations are archive and store in the same manner as emails. This make easier to search within their chat logs and to have all users convesations centrally store no matter what computer is use.
Offline Messaging: Even though a conctact apears offline, users are able to send him/her an instant message. The sender's offline contacts will receive these messages when they next go online.
Games: There are various games and applications available that can be accessed via the conversation window by clicking the games icon and challenging your current contact.

Download Yahoo! Messenger 8.1