A world/society simulator with nested hexes, down to the individual person/tree and out to a whole continent. multiple people can form factions (or leave them), trade, go to war, claim territory. forage, chop trees, grow food, research tech trees. hierarchies are emergent based on individual and group choices, "borders" aren't real. buy loyalties are.
I'm currently having my mind blown. development is moving stupidly fast. we'll see where it hits the wall of "idea sounds incredible on paper but isn't feasible in software or UI" - haven't gotten there yet!