A zero-player game (see also Progress Quest) but instead of dungeon crawling try Car race simulation. A ZPG version of gran turismo or forza would be awesome.

The player would start with some cash; they could either then let the ZPG run, or they could have limited input such as buying the first car. The ZPG would then do motoring tests, racking up badges for passing, and then gaining licences, and then enter races.