Forza Horizon 2 players on Xbox One can expand the selection of available in-game cars for free right now, but only for the next eight days.
A pair of Porsches--the 2012 Porsche 911 GT2 RS and the 2012 Porsche Cayenne Turbo--can both be downloaded for free in Horizon 2. However, you will need to first download the Forza Hub app from the Xbox One's store. If you already have it installed, you can simply open it up and look for the icon promising you "Two Free Porsches." That'll direct you back to the system's store, where you can download the cars.
2012 Porsche 911 GT2 RS
Last month, Microsoft released a Porsche-focused expansion for Horizon 2. Part of this included new achievements, three of which will be available to all players by downloading these new cars.
If you're interested in the freebies, you'll need to get to grab them by Friday, July 24. The Forza Hub app is fairly useful for Forza fans, if only as an easy way to access Forza Rewards, which can get you in-game currency and cars for being a devoted player of the series.