While I'm currently running an alt-history campaign and mostly run Call of Cthulhu, I've been rolling this idea around in my head for a while now and want to get it out on paper (so to speak) and maybe eventually run something weird and sandboxy with it.
Khorlhossa being an extremely metal-poor world, most armor is composed of leather, wood, ceramic or bone, while weapons are largely made from wood, bone, obsidian, or the chitin of insect-like monsters. Weapons and armor of steel are extraordinarily rare and prized things, treated as if they were magic in their own right.
Most inhabitants of Khorlhossa belong to the Church of the Grey and Silent Lord, a grim figure that punishes cowardice and rewards those who exemplify the adage that "Might Makes Right." However, many pay only lip service to the Lord, secretly serving in cults venerating various demons that seduce with promises of easier living and great wealth.
There are few creatures on Khorlhossa that would be considered "ordinary" animals; among these the rylbacks (bloated, herbivorous reptomammals that graze on the thick, spongy moss of the former sea beds, hunted for meat, fur, leather and bones) and skrane (long-legged bipedal reptomammals used as mounts) are the most common.
Most of the biosphere of Khorlhossa is composed of Monsters and Demons, the difference being whether they are born of the world or beyond it.
Monsters are frequently the misbegotten spawn of ancient sorceries, pent up since time immemorial in ruined
Demons are drawn to Khorlhossa from the Unforgiving Dark, summoned by sorcerers and warlocks seeking temporal power through pacts and arrangements with the powers beyond. While many Monsters have only animalistic intelligence, Demons are invariably intelligent, scheming, venal creatures, making them far more dangerous.
Some Monsters are vulnerable to weapons composed of certain materials such as wood, glass, bone, etc. All Demons are vulnerable only to weapons of steel.
Khorlhossa as a setting draws inspiration from Geoffrey McKinney's Carcosa setting, Edgar Rice Burroughs' Barsoom, Tekumel, the Dark Sun setting for AD&D 2nd Edition, and Robert E. Howard's Hyborian tales. When and if I run anything in this setting, it'll likely be with the Lamentations of the Flame Princess ruleset.