@ingalacornicum These are some GM-less games that need no preparation (for one shots, not campaigns):
* Deeds, not Words (I wrote this!), a game about she suffragettes: http://hardcorenarrativist.org/items/deedsnotwords
* Ribbon Drive, mentioned elsewhere, a fantastic game about road trips: https://www.drivethrurpg.com/product/114059/Ribbon-Drive
* Fiasco, a Coen brothers-style story game: http://bullypulpitgames.com/games/fiasco/
* Night Witches, a game about female pilots in the 2nd World War (also works for campaigns!): http://bullypulpitgames.com/games/night-witches/
thank you all for the amazing recommendations, i'm gonna them all check out!!
@hardcorenarrativist @Yoric @rafu @hawkjohenson @phyrry and everyone else!
@ingalacornicum I realised a bit too late that Ribbon Drive *does* need some preparation! Each player has to bring a "mixtape" with music (the music is extremely important in the game and drives the narrative, to an extent).
And while at it, I might as well recommend The Skeletons, a double reversal on the dungeon crawling idea:
http://bullypulpitgames.com/games/the-skeletons/