cars won't be good enough for you yet but I think it will be just like Forza but a bit harder to learn when it is released. Assetto Corsa is a total unknown in terms of gameplay and structure right now so count that out until we know more.
Auto Club Revolution is similar, although its a mmo.
Its free.
You unlock cars, tune them up, customize them and race. Thats basically describing forza
http://autoclubrevolution.com/en/
Owch not a good recommendation there. There is very little to do in ACR compared to the huge world of Forza and cars still hit each other when not touching and make weird clanging noises and start races upside down.