From publisher blurb:
Bloodwraith is a stand-alone, self-contained fantasy setting for any roleplaying game system, specifically ones that focus on gritty or low-tech fantasy. This book is about the setting and style of bloodwraith, with extensive time spent on plot, setting, and tone. Mechanics and die rolls are informed by the systems used to play.
The adventure challenges of this game world focus on survival and dealing with the world in front of the characters, than dungeon-delving and super-heroics. That won’t stop people from doing those things in this world, but that is not the intent of this game world.
Any OSR system like ACKS, Dungeon Crawl Classics, Osric, or Swords and Wizardry are ideal for use with Bloodwraith, if players do not want to use the Bloodwraith rules system.