Call of Cthulhu is one of the great role playing games. There is a set of free quick start rules available on RPG Now.
Horror
Shaun of the Dead Card Game
Shaun of the Dead is free card game based on the very funny movie of the same name.
Reanimation Zombie Survival Card Game
Reanimation is very highly rated at Board Game Geek. And it is free.
Dice of the Living Dead
Dice of The Living Dead is a free print-and-play zombie survival horror game.
Cthulhu: The Great Old One Card Game
Cthulhu: The Great Old One is a simple, free print-and-play card game.