Hail and well met!
I thought I would share some of the work I’ve done so far on the game I’m writing for this jam.

So as the title mentions, the game is GM-less, and as such entirely based on cooperative role play and world building. In this respect it’s based on the same principles of Come Rain Come Shine.
The basic premise is that the Players have a shared pool of Adventurer Characters, who have set up and manage an Adventuring Guild.
Quests are generated using roll tables, and then played out in a series of stages using prompt and rolling for Complications along the way. This is all pretty much identical to CRCS.

Where it differs from CRCS is that I’d like to add a mechanic for defeating enemies, like in classic fantasy RPGs, but without lots of crunch like damage types, health points, etc. 
The idea at the moment is to have an enemy require a certain number if successful actions made against them in order to be defeated. The Players each describe what they do on their turn, deciding if it all happens simultaneously or not. Then the enemy Action is determined by another roll table, on their turn. 
What I like about this is that it keeps things narrative and player focused, while also allowing for combat scenarios as well as any other form of “defeating” (e.g. sports, rap battles, etc.). I’m thinking of calling these Challenges, and leaving it up to the Players to decide when they happen during a Quest. 

For every successfully completed Quest, Players earn in-game rewards, but also Adventuring Points which they can use to gain free successful Actions. 

I have more notes, but would love to know what others in the jam think!