Not a world, but phun ;)

I really would like to recommend anyone to have a look into phun.

What is phun?

Its a 2D physical sandbox, wich is very intuitive and just... fun.

As kids we used to sit in a sandbox, build carparks, castles, battlefields or whatever came to our mind. In phun you may find a bit of that feeling back.. you can experiment with a lot of stuff there, like a watersimulator, motors, gravity, springs, explosions and a lot of things more.

Its easy, nice and colorful.. it should be fun to build some "crazy machines" or whatever together with kids. Soooooo enough telling, go have a look :)

http://www.phunland.com/wiki/Home

or check it out on youtube:

http://www.youtube.com/results?search_query=phun&search_type=