Google has released their "Virtual World" dubbed Lively into beta. I took some time to play with it today and figure it out. Essentially it functions as a series of chat rooms with 3D engagement. Not unlike Second Life, Meebo or Habbo Hotel. You can chat with friends, make new ones, etc.
The key differentiator between Lively and the others is in its ability to live within a webpage. You can embed a room within a blog like so:

Lively currently won't work on non-Windows platforms, and like many other betas, it is lacking certain elements like a more robust list of furniture, clothes, etc. But there's good news. It's completely free... So far.

Jon