I am currently not a Playstaion+ subscriber, but by the end of the day I will be.
Every month Playstation+ subscribers can play some select featured titles for free.
Next month, the list of free titles for PS3 include:
Batman: Arkham City
Castle of Illusions starring Mickey Mouse
Full list of free games in April
For PS4 owners who still cling tightly to their PS3s, there was a coupon booklet when you bought your PS4 that includes a free month of Playstation + that expires on 3/31.