Spiralis
Spiralis is a rules-light game of eldritch mystery and cosmic horror, inspired by Graham Walmsley's Cthulhu Dark and the Powered By the Apocalypse family of games. It is tailored to run mini-campaigns (2-6 sessions in length), but also works well for one-shots.
Creating Investigators takes just a few minutes, and every roll of the dice, whether taking Action or making a Stat Check, propels the story forward. Keepers and players have distinct agendas that will focus play on the types of stories you want to tell, and ensure that everyone at the table has an equal chance to contribute to the fiction.
Spiralis features extensive Keeper advice, including a questionnaire that will help you construct compelling mysteries for the players to explore, while not entirely leading them by the hand at every step.