Inuma: The Red Book

From the introduction:

Inuma is a toolkit to build fictional worlds and then play out stories in those worlds. Each of these worlds are self-contained and focused on the characters you will create for that world. When thinking of this concept, imagine "worlds" like the areas explored in your favorite novels or movies. The "world" of those stories might be entire planets, but are much more likely to be countries, cities, islands, or even one forest. What we call "world" in Inuma is the equivalent of a game's "play set," but for stories.

User summary:

The Red Book focuses on cooperatively creating and detailing the world, or setting, of the campaign. No specific genre is contemplated in the rules.