Forza Motorsport 7 will be available worldwide on October 3, but if you want to try it out even earlier, you can try the Demo which will be available for download on September 19th both for Xbox one, and Windows 10 PC. It’s a demo, hence it is limited to

Three unique racing experiences,
You can drive the “Forza Motorsport 7” cover car – the Porsche 911 GT2 RS – on the new Dubai circuit.
Nissan NISMO GT-R LM is available for a race at the Nürburgring Grand Prix circuit.
You can also navigate through the Jebel Hafeet Pass, one of the most famous driving roads in the world.
Apart from Porsche, you can also try the Mercedes-Benz Tankpool racing truck.

When playing the demo, you can choose the difficulty level, and for PC gamers, you can adjust the performance options to what it suits the best. These options are great if you have the plan to buy the game or the Xbox One S or Xbox One X bundle.The Ultimate Edition will get an early access on Sept. 29.

Source: https://news.xbox.com/2017/09/07/fm7-gone-gold-and-demo/

When you finally buy, you also get Pagani Huarya, Porsche Cayman GT4, Plymouth Barracuda, Nissan GT-R and Block’s own custom-built Ford Mustang “Hoonicorn. Check out the video below:

https://youtu.be/_PKL3323wkQ

More at Xbox Wire.