De Profundis

De Profundis, Letters from the Abyss is an epistolary RPG of lovecraftian horror written by Michal Oracz.

Player characters exchange letters in which they discuss their eerie and frightening experiences and their investigations into the occult and horrific that lies hidden just beneath the mundane visage of the world around them.

There is no system per se, and play is essentially freeform, but the game does provide a template and general guidelines for creating a story of gradually creeping horror and insanity.