Google Talk

Google are not sleeping these days - they (like Yahoo) have just launched their answer to Skype - although you have to have a Gmail account to use it at this point - is looks like a really clean application ~ 1mb although there does not appear to be any "wow" features as far as I could see.

"They say talk is cheap. Google thinks it should be free. Google Talk enables you to call or send instant messages to your friends for free–anytime, anywhere in the world. "

Check it out:
http://www.google.com/talk/