It was during Microsoft's E3 conference that they initially announced that they were copying a bit of what makes PlayStation Plus so alluring to consumers. Starting from July until the Xbox One releases in November, they will offer two free games a month for Xbox Live Gold members.
The promotional page is live and shows off Fable III although that is actually a game not included in the promotion's time span. Each month a free game will come out on the 1st and 16th. July's two games are Assassin's Creed II and Halo 3.
Just like Sony's Instant Game Collection, these titles are only available for a limited time as free downloads. Of course, only Gold members can take part in nabbing them as well (it is unknown if losing Gold status will remove the games). Also, this is not a new facet of Xbox Live Gold but simply a way to drum up excitement until the Xbox One launches which is when the promotion will end.