I realized while I was making that story prompt generator a while back that what I had really been trying to do is make prompts for multiple people to bounce back and forth and build on together. I've also always enjoyed forum roleplay threads over tabletop games with dice and stats and what not, so this is a LOT more freeform than a typical tabletop game, and what rules there are just make it playable/portable across pretty much any forum/message board/link aggregator website.

I made some prototype rules for this game, and the community I made for it is linked. Basically you have an "Editor" (Game Master/Dungeon Master) who guides the writers (players/characters) through creating a world and their characters, then regularly adds a chapter prompt that they have to write a chapter for their character for. It's not a long time commitment, I was thinking to playtest a story for maybe every other day or every two days for the shortest story structure (5 chapters). It's all designed to take place in one forum post, with top-level comments for OOC, world building, character creation, and the chapters. Also, if this does just turn into a freeform r/writewithme clone, my feelings won't be hurt; it will be cool to have helped create a community no matter what it looks like in the end.