From publisher blurb:
What if the original roleplaying game was inspired by colorful superheroes rather than Tolkienesque fantasy?
GUARDIANS is a super hero retro-clone compatible with the original fantasy roleplaying game and subsequent editions, and other “OSR” games that follow in the mould of the original game like Swords & Wizardry, Adventurer Conqueror King, Labyrinth Lord, and Warriors of the Red Planet. If your tastes run towards super-powered four-color heroes and villains you’ve found the right book. In a tradition inspired by the psionic abilities of Eldritch Wizardry and the mutants of Metamorphosis Alpha or Gamma World, even a first level Guardians character begins with mighty powers!