FriendsHangout launched their Virtual World Builder today. It uses the Unity 3D platform, so it runs right in your browser. They have a small virtual goods store and a developers program. Avatars can be created with Evolver and then exported to FriendsHangout.
I didn't have much time to do more than create an initial world, try out the terraforming and add a few items, but you can check it out here as a guest, or view this short video.