Greetings truckers!
If you are still unsure whether to take the risk and buy the game for
fear of technical incompatibility, we are happy to announce the
availability of a free American Truck Simulator demo.
Try it out to make sure the game will work on your computer before
making the purchase decision. You can grab it from Steam now, just as
the game itself.
The demo is limited by the number of jobs taken and only contains the
state of California, but technically it's identical with the game
itself. If you purchase the game after playing the demo, you can
continue driving where you have left off, as the save game stored in the
demo mode is compatible with the full game.
Source: http://blog.scssoft.com