I have a account at There world but i never really explored it. http://www.there.com/
It is a nice little world that was closed for some years but now is run again.At the time i never really did any exploring so i have started out travelling in my jeep all over the place again. Lot of places i have never seen.
The physics engine is great and that means you can really do stuff with vehicles. I love the look of the avatars.
Maybe now when we have seen many virtual worlds There gets its chance again. It have a very clean look and runs on anything but the software have not been updated since Windows XP. Sorry to say. And I got the client running so and so on Linux too. My hope is that it all goes in the public domain. This is a gem of software that deserves more. I would love to run a There world. The things you could do..