Microsoft Store has announced its free Games with Gold for April. Some are available on the first of the month, while others start later this month. Requires Xbox Live Gold subscription ($9.99 for 1-month, $25 for 3-months, or $60 for 12-months).

April titles are as follows:

4/1 to 4/30: Vikings: Wolves of Midgard for $0 ($40) [Xbox One] 

4/1 to 4/15: Dark Void for $0 ($15) [Xbox 360 and Xbox One]

4/16 to 4/30: Hard Corps: Uprising for $0 ($15) [Xbox 360 and Xbox One] 

4/16 to 5/15: Truck Racing Championship for $0 ($60) [Xbox One]

March titles that are still available:

3/16 to 4/15: Vicious Attack Llama Apocalypse for $0 ($15) [Xbox One]