Starting Sunday (December 1st) Gears of War (Normally US $19.99) will be free for Xbox Live Gold members through December 15th.
Then on December 16th, Xbox Live Gold Members can download Shoot Many Robots (Normally US $9.99) for free.
Microsoft’s “Games With Gold” program gives Xbox LIVE Gold Members 2 free games to keep each month. A new title will be available the 1st and 16th of each month. Microsoft also revealed that this plan might come to Xbox One users in the future.
Source: Major Nelson