Book of Exalted Darkness
Fantasy (High Fantasy) Fantasy (Science Fantasy)
The Book of Exalted Darkness is two things: a holy decopunk campaign setting (think Rocketeer or Sky Captain and the World of Tomorrow) and a sourcebook for playing evil characters in D&D 5E.
Together they make for a slick and stylish campaign setting with a bevy of meritorious NPCs paired alongside a grimoire of vile and forbidden evil, the PCs gaining a little more edge through their trickery or perversion of the very technology that makes the world so unjust.