You probably know about OSE Demon Month, which just launched. There's a lot of cool looking books, including our own Emporium of the Damned.
We wrote it to add a lot of material to the Demonic Grimoire, and it has many locations and agents for connecting to all eight planes of Hell., over 60 demonic weapons, relics, grimoires, and geegaws, corruption mechanics that physically (and spiritually) transform characters, rules for gaining dark boons and dire favors in exchange for your soul, hell mounts such Havoc Goats, Charcoal Rocs, Bone Serpents, tons of demonic, demented, and otherwise damned NPCs, orders, sects, cultists, and other unsavory collectives. There are also some none-too-subtle Motörhead references if that helps!
If any of that sounds dope, check it out: Emporium of the Damned