It's like Skype, except calls to regular phones are free (at least in 2012). This is NOT Google Voice, which gives you a phone number. You can voice chat or video chat, and I just discovered that calling landline or mobile numbers in the US & Canada from the US or Canada is FREE.

https://www.google.com/voice/b/0/rates

I can do this from right within Gmail where it's labeled as "chat" in the menu on the left.

More info: http://www.google.com/talk/start.html

Thought some might find it interesting, especially with the free calls.