For almost a year now, Xbox Live has been offering Gold members two free games a month as part of the Games With Gold Program. For the last many months, the first half of the month has been a bigger title that was originally released physically, along with the second half being some XBLA game. However, this month, we have received the XBLA game first with Dust: An Elysian Trail.
As of right now, you can download Dust: An Elysian Trail at no cost as a Gold member on your Xbox 360. This will be available through May 15 and starting on May 16, you will be able to get Saints Row: The Third as your other free game this month. Dust: An Elysian Trail released over a year and a half ago, while Saints Row: The Third released about two and a half years ago.