Google Talk

http://www.google.com/talk/

Google Talk is a lightweight Jabber-based instant messaging client with voice capabilities. Google Talk is easy and intuitive to use. All you need to make free calls is an Internet connection, a microphone, and a speaker. After you download Google Talk, sign in with your Gmail username and password. Invite your friends to download Google Talk, and once they do, you'll be able to talk or IM with them instantly.

Google Talk currently does not encrypt chats or calls. When you use Google Talk, you can choose to have your IM chats stored locally on your own computer so that you have a chat history. Google does not collect the content of instant message chats or voice conversations.

User Review:
This application has no bloat, no ads, no unnecessary side-installations. It's almost perfect.

Simple and sweet. Finally a communication client without the bloat. Great product - even in it's current beta form.

Very nice software... this has a lot of potential. Simplicity and functionality both at the same time. I'm sure there's more to come.

Simple and to the point. I like it. I'd like more corporate features also, or a separate corporate client. Then I can bail on msn messenger for good.