Forza 6 Apex Open Beta was released today for Windows 10 / Windows Store. Download is 18.8GB.
As this is a DirectX 12 game, you'll need Windows 10, and you must be running build 1511 or later.
Can use Keyboard or Gamepad, no steering wheels yet.
https://www.microsoft.com/en-us/store/games/forza-motorsport-6-apex-beta/9nblggh3shm7