A racing simulator. http://www.rfactor.net/ Google helps...

THO if you want it to actually be good, you need proper wheel-set, realfeel plugin installed for proper FFB and a good mod, like Historic Touring car mod, it's the one I was using when driving with Alpine, haves some nice Fords too.

Sadly majority of the mods have crap physics, but some of them are very good, like the Historic one. If you see a mod what says physics produced by Niels or whit his tool it probably is great.

The Nordschleife is downloadable content too.

rFactor as itself is just horrible, but with some tweaking it's one of the best things on my PC currently.

-EDIT- Quite good video I think:
http://www.youtube.com/watch?v=7_-Tso6fxcQ
It's the "physics genius" Niels driving Escort mk1 BDA in rFactor, look up for other of his vids too.