Drop

from the introduction:
In DROP, you and your friends will write a story. To keep this story from devolving into silliness too quickly, its plot is carefully structured.

You will write a story in five parts: a preparation phase where you discuss the basic parameters of the story, and four story acts. Each player will control one crewmember on a starship that’s been summoned to a planet. The crew will descend to the planet’s surface, explore a mysterious landmark, then run for their lives.

You can also play this game yourself, by taking on all the characters’ roles. The game assumes that the players are friends, and that they will freely discuss the ongoing story among themselves. This is not a competitive game, though you can screw over the other players.

user summary:
Drop is a semi-freeform story game in which the players take on the roles of explorers descending to the surface of a planet and encountering a nameless horror.