A couple of years ago I came up with a MMORPG concept where it was up to the people in the world to collectively devide the content.. The idea was, here is a world, now you all decide what to do there. IT was inspired by Neil Stephensons book "Snowcrash". Well, that place exists and it's called Second Life.
This is a world where all the content is user created, and it's got a super powerful interface there for you to do just that.. you can create any object you can imagine and even make the object do stuff by scripting its behaviour. You can upload textures and sounds and there is an entire economy inside the game for pre-made objects and textures..
It's pretty incredible, but it has it's negatives. First off, its complex. Normally I would love that but I just don't have the time to devote to learning all the details of the interface and spending the time creating stuff. Secondly, I'm not sure I had it tuned right, but the graphics performance wasn't that great when I tried it.
The cost is just $9.95 total. You pay once and you're in. If you'd like to buy land in the game, you can pay a monthly fee and 'lease' land in the game. There is also a 7 day trial (which is what I did). The download is small and I highly recommend you try it out and see where the future is. A world like this is the future of networked entertainment, I guaranee it!