Present Day Cthulhu (Multiverse Adventures)
The Cthulhu Mythos for the Multiverse Adventures system ( the Fate Core version is here ). This book includes a present day Cthulhu setting and a compact version of the Multiverse Adventures rules¸ so you have everything you need to confront cosmic horrors in one place.
This 164-page book provides Mythos locations¸ Monsters¸ NPCs¸ the Dreamlands¸ an example scenario¸ several cults¸ a secret history of the Earth¸ and uncanny Mythos tomes¸ with the spells and powers they contain.
The Earth is doomed and there is nothing your puny efforts can do to avert its fate¸ but it's your duty to try!