Forza Horizon players can now take full advantage of Xbox SmartGlass on their Windows 8 computers. Microsoft launched Windows 8 on October 26, 2012, and official support for the Xbox 360's second screen-oriented SmartGlass feature arrived along with it. Forza Horizon was pegged as one of the early games that would support the new feature, and a newly released Win 8 app allows you to do just that.
The "SmartGlass Experience" for Forza Horizon uses your second screen as a map of the game's open world, complete with the "locations of special items such as smashable upgrade discount signs, new race events, and more," according to the press release. I know that some map content is unavailable until you pay real dollars to unlock it; it's not clear if the SmartGlass map includes that stuff as well.
Although the Forza Horizon support for SmartGlass is exclusive to Win 8 right now, expect to see other platforms added soon as well.