Just gonna post this Gamespot list
since it's easier than trying to link a bunch of titles.
Pac-Man Championship Edition 2 free on Steam, XBox, and PS4
Total War: Shogun 2 free on Steam starting on 4/27
Polyball free on Steam
Uncharted: The Nathan Drake Collection and Journey free on PS4 (this isn't the usual monthly PS Plus giveaway, but separate freebies in addition to that)
Crackdown, Crackdown 2, and Too Human free on XBox
Various other sundry things through lower-profile services