Tools of Terror and Blood (2013)

From publisher blurb:

There's something lurking in the shadows...

As great as the OGL d20 systems are, few lend themselves well to horror; the game has to often be disregarded. With Tools of Terror and Blood, we hope to give GMs and players who want to bring the feeling of a supernatural thriller or a good slasher flick to the gaming table some game-mechanical support through 19 new feats and three new talent trees.

The lead designer on Modern Basics: Tools of Terror and Blood is Steve Miller, an RPG industry veteran who has contributed to dozens of supplements for horror-themed games, including ones for the Ravenloft setting from TSR/Arthaus and the classic Vampire: The Dark Ages and Werewolf: The Wilf West games from White Wolf.

Although designed with OGL Modern in mind, much of this supplement is easily adaptable to other games that use the OGL d20 system.