"Grimoire of the Gods"
From the title page:
Within this grimoire are descriptions of immortals and religions. Regarding F.A.T.A.L., it is a collection, notarization, and study of metaphysical beings. Everything that MMs need to know in order to introduce gods to their games is included in this book. When possible, information concern- ing gods has been based on mythology, not whim.
Like every work but the main rulebook, this is unfinished.