Yahoo Messenger is a free service that allows you to see when friends come online and send them instant messages. It can also alert you to new e-mail in your Yahoo Mail or Yahoo Personals account, or when you have upcoming events recorded in Yahoo Calendar.

Key features of Yahoo! Messenger:
- Connect with all your friends
Instant message with a world of friends who use Yahoo! (or Windows LiveTM Messenger).

- Stay in control...24/7
Decide who sees you online with stealth settings.

- Share away
Swap photos and files (huge ones) in real time. Plus enjoy voice calls and webcam video.

- Yahoo! Calendar
Stay organized and get calendar alerts.

- Contact Search Bar
Quickly find a contact to IM, call, SMS and more.

- Address Book
Synchronize all your contact information.

- File Transfer
Share files with friends instantly.

- Chat Rooms
Join a live, group chat room to discuss a variety of topics.

- Make Calls From Your PC
Make free worldwide PC-to-PC calls, plus free voice mail.

- PC-to-Phone Calls* - New!
Call regular and mobile phones for as low as 1¢/min.

- Phone-to-PC Calls* - New!
Get a phone number for your PC so friends can call you.

- Connect on Yahoo! 360¡ã - New!
Stay up to date with friends' blogs, photos, and more.

- Take Yahoo! with You
Send and receive IMs on your mobile phone.

- Webcam
Share live video with friends and family around the world.

- Conference
Exchange text messages with multiple people in one IM.

etc.