Crossplay platforms:

Forza Horizon 3 will support cross-play across multiple platforms. It will be possible to play together with your friends on Windows PC and XBox One. Please check out all the details on the game's official website!

Summary:

You’re in charge of the Horizon Festival. Customize everything, hire and fire your friends, and explore Australia in over 350 of the world’s greatest cars. Make your Horizon the ultimate celebration of cars, music, and freedom of the open road. How you get there is up to you.