Here is a list of free games available:
Uncharted: The Nathan Drake Collection
Uncharted 4: A Thief’s End (PS Plus only)
Dirty Rally 2.0 (PS Plus only)
These games are available for free for a limited time through digital downloads from April 15 at 8pm PDT through May 5, 2020 at 8pm PDT.
Once you redeem the games, they are yours to keep.
There are also 95 Free-to-play games from Play Station Store available.