Horde of the Dead is a free print-and-play game of zombie survival.
The entire run of Ray Bradbury Theater is now on YouTube.
Lamentations of the Flame Princess is an old school RPG of “fantasy adventure and horror.” The link is to the free version without illustrations. The illustrated version apparently has some rather adult and disturbing illustrations.
Call of Cthulhu is one of the great role playing games. There is a set of free quick start rules available on RPG Now.