GoogleTalk

Google Talk is an instant messaging service. It provides both text and voice communication. The instant messaging service is colloquially known as "gchat" to its users.

Using Text chat You can:

• Write instant messages: share quick thoughts in real time
• Update your status: see if friends are around and what they are up to
• Transfer files: instantly send and receive files, pictures, and more.

Using Voice chat You can:

• Communicate in free long distance: make PC-to-PC calls to people anywhere in the world
• Make audio conferencing: talk to multiple people at once
• Have Gmail integration: chat with your friends on Gmail

Here is an interesting link, which can help You to know how to use Google Talk: http://www.google.com/talk/start.html
And here are news about Google Talk: http://www.google.com/talk/whatsnew.html

Next time I'll tell You about Google Chat