We are about halfway through May, making the second round of Games with Gold games available to Xbox One and Xbox 360 owners. As long as you subscribe to Microsoft's Xbox Live Gold, you can download games monthly as a bonus.
Xbox One owners can look forward to Costume Quest 2 being available between May 16 and June 15, in addition to Defense Grid 2, which has been available since the first and will continue to be available until the 31st of May.
Xbox 360 owners will be able to download Peggle between May 16 and May 31st. Grid 2 was previously available, however it has been phased and replaced by Peggle.
Both Grid 2 and Peggle are backward compatible, making them accessible on the Xbox One.