Driving sim Gran Turismo 5 will allow users to create their own tracks. Here's how you build one, then go race on it!
You can't build your own course out of thin air, of course. There's six years worth of rendering on those stages and roads, so you won't be playing LEGO Gran Turismo, making tracks in the shape of a Final Fantasy character. Instead just pick which of a certain stage's many alternative routes you want to combine, choose a time of day, set the weather, the stage points then you're good to go.
Can't wait to make a NASCAR track in the middle of the desert and fill the race with combi vans...