The first episode of Telltale's series of Back to the Future adventure games is now free to all. You can download it from the Back to the Future site. You'll need to sign up for a free Telltale account first, but once that's done, the game is yours. Episode 1 is called "It's about time," and has Marty travelling back in time in the trusty Delorean to save Doc from trouble. Episode 3 of the 5 part series came out last week.
Back to the Future: Episode 1 is now free