Make your own mythos!
The game is called Silent Legions and it is an old-school D&D take on Lovecraftian horror. Mr. Crawford designed the game for sandbox style play, and the jewel of the book is the chapters on mythos creation. The PDF is worth it for the rules on generating your own elder gods and cosmic horrors for any campaign. I've read through the rules and I am currently starting a play-by-forum game. The rules are heavily influenced by original edition D&D with a skills system added to it. The adventure creation system is perfect for GMs who need to create campaigns quickly.
If you are a fan of horror and old-school rules check it out.