GURPS Monster Hunters

From the introduction:

You know, anon, there are things out there. Creatures that go bump in the night. Beasts, born of the vile darkness, haunting your fair cities, searching for prey. And some... some aren’t even of this world. Aliens such as Greys or Devourers, attacking innocents, harvesting them for their own ends. And those that are aren’t much better, vampires, werewolves, and other such beasts, creatures of the night. But you’re here now, Anon! You’re going to save everyone. But you can’t do this alone, and not as- well, okay, you might be able to do it as you are.