From the introduction:
Writers in the Darkness is an immersive, Lovecraft inspired horror RPG played by writing physical letters between two people. The GM writes letters as The Writer, a character who is stuck in a terrifying situation, desperate for guidance to save them from a nightmarish threat. The player responds by writing letters as a friend, ex-lover, former enemy or associate of The Writer, offering advice and guidance to try and help them escape the situation with their life and discover the truth behind what is going on.
For this game the Gamemaster (GM) will require a 20-sided dice (d20) and six-sided dice (d6), while the player will need no dice. They will both require writing supplies and the ability to send letters through the post to each other. The game can also be played over email or any other medium that allows the sending of letter-like messages if they prefer this