"The early modern era, into which cosmic horror breaks through."
Lamentations of the Flame Princess is James Edward Raggi IV's weird-horror OSR game. The rules are a B/X D&D derivative, but the presentation is different: dark, adult, often shocking horror fantasy. Magic here is dangerous and alien, and treasure is a curse. Famous for its outstanding standalone modules and uncompromising tone.
Not an invented world but a real, roughly 17th-century Europe — filthy, superstitious, brutal — into which Lovecraftian and Howardian cosmic horror intrudes. Magic is rare and warps the world; the supernatural is always alien and wrong. It plays as historical horror or as grimdark fantasy with teeth.
B/X core with skills
d20 to hit, B/X classes and levels, but with a Specialist (thief) and a d6 skill system. Compatible with old-school modules while a touch more modern in the details.
Dangerous, alien magic
Spells aren't push-button fireballs but something wrong and risky. Magic breaks reality, and often the caster with it — exactly the weird tone the whole game sets.
A real historical Europe
Set in an actual early-modern era with dates and places, into which cosmic horror erupts. The grounded history makes the supernatural doubly unsettling.
Free no-art version
The official 'Rules & Magic' in a no-illustrations version is a free PDF (LotFP art is often NSFW). The full rules with a zero-cost on-ramp.
Open in Session Zero to let every player vote and see the results.