Update #2: The Fable 3 giveaway was intended by Microsoft. It's part of a new two-free-games-a-month deal that will, at some point, include Halo 3 and Assassin's Creed 2.
Update: Xbox Live Silver members cannot take advantage of this and are charged 3600 Microsoft Points for the game.
Original story: You can grab the full Fable 3 game from Xbox.com now for free.
All you have to do is select "use Microsoft Points" when asked how you'd like to pay. The cost is 0 Microsoft Points and when you "confirm" the deal, hey presto, the game is yours. Thanks, Eurogamer forum!
This is probably an accident on Microsoft's behalf rather than special gift to go with its E3 conference this afternoon.
Fable 3 was the quickly made follow-up to Fable 2 on Xbox 360, and was pretty good.
Lionhead recently revealed Fable Anniversary, a remake of Fable 1 for Xbox 360. Presumably Lionhead is also working on a fourth Fable game for Xbox One, although not a whiff - besides some job adverts and hiring a new boss - has been given.