Occult and esoteric books in general, such as "The Kybalion" (Hermeticism), "The Book of the Dead" (Egyptian), "Liber AL vel Legis" (by Aleister Crowley, Thelema), as well as grimoires (such as the "Book of Saint Cyprian"). While there are tons of movies and TV Series that directly adapts biblical stories, I feel that there are so few (if there's any) cinematographic works adapting esoteric, occult, pagan books (from belief systems such as Gnosticism, Wicca, Rosicrucianism, Hermeticism, Luciferianism, Thelema, Goëtia, and so on). I even tried to ask AIs to list movies and TV series adapting such books, and every single listed movie (such as The Matrix) is not a direct adaptation. They don't even mention these books (in best cases, The Matrix merely alludes to hermetic principles such as "the Universe is Mental" (i.e. the scene between Neo and the kid that says that "the spoon doesn't exist").