In the Thursdays games, we have played a few games that took no preparation and sometimes not even a GM.
Examples are Goblin Quest, Everyone is John and Munchhausen.
This was quite useful. When nobody had anything prepared, we still managed to organize a game.
So I wanted to outsource a question to everyone.
What other games; that take no or little preparation, or that don’t even need a GM; do you know? And ideally also that you would recommend 
Lady Blackbird is great
Not 100% sure, but I think that was the first Indie game at the Thursdays indie-group ever?
dm-ed by @Alrik
I guess you will like Technoir a lot
(look out of the Transmissions)
there is also a Mechnoir variation, but I have not played that one yet
MAID RPG works really well for that
it utilizes tons of tons of random tables really well
(that is why) you need the hardcover though, if you want to play it
(some crazy folks also homebrewed an Eclipse Phase MAID RPG)
The Mountain Witch also comes to mind
@GJsoft dm-ed that once
Ten Candles also works really well
I think that one has also been played with a thursdays-indie-group at least once
also there are Classroom Deathmatch and Panty Explosion Perfect (the name is a pun on Engrish)
have not played the first one, but both are basically dm-less
(both games are from the same developer)
My Life with Master also counts I guess
but it is too much of a simulation for my taste
(to be fair I only played it once)
Shinobigami could also be run with little to no preparation, if the player’s had already played it / or the dm knows it well
I also want to mention SHERPA (the web version is free)
a rpg, that was designed so you could play it at picknicks
… but it won’t give you a free plot
(thanks to @H for introducing me to that … proved to be super-useful for my Post-Lockdown-Garden-Picknick-Games ™ ^^)
Last Thursday was fun it totally look like I have to attend more often - sounds like some interesting crazy stuff.
Available at Planet Harry: Fiasco
Oh, and this great compilation of weird indie rpgs: Level 1 (Free RPG Day 2020)
@PatrickD: we are happy to hear, feel free to come!
I cannot bookmark this post enough, definitely will check these and give it a try myself!
Also here is a game I’ve tried a few times - Lasers & Feelings - it literally doesn’t require any preparation, as the players roll for the plot together. Only downside is (based on my experience) that the GM needs to have some experience and good improvisation skills to fill up the story on the spot and the figure out some additional rules, if necessary.
Furthermore, the base rules are so flexible that it can be applied to almost any settings - and the fans already made many variants (from Star Wars through Wild West to Muppet Babies). Once even I’ve made my one version based on an obscure british comedy
Finally, WAAAGH! Da Orks also worked quite well. It is not as rules light as the other games in this post, but as it is about playing with stupid ork space barbarians, you don’t really need a plot - the stupidity of the characters write their own tale
All of them? :b
But seriously, we’ve played a bunch of these over the years. I kind of like Murder of Mr Crow; not tremendously deep, but pretty fun every time we ran it.
Allo Allo is sooo awesome 
This makes me extremely happy. Have a great time!
If you are interested, I can run another game sometimes