If, like me, you have your roots in kart racing then you will love this.
To me they have managed to get the feel of the thing just right but without the bruises!
http://www.kartracing-pro.com/ It is currently at Beta5 and still being developed but there is a move afoot to start a European League and have some organised races. This can only accelerate the developments in my book and one of the things that they have to sort out is the starting procedure, which is a dog's breakfast.
There are three fixed gear karts and one 125cc gearbox variety. Personally I have always felt that gearboxes are ok for trucks and anything that you use to tow your racing machinery to the circuit.
I find that it sharpens me up for the lumbering PnG cars but because it is so much of a chalk and cheese comparison I do not find that one leaks into the other.