I am building Eremoterra, this experiment of trying to make a game out of an MCP (to learn MCP stuff, but also had a lot fun designing the game).
You play in your own agent. The server returns a fact sheet for the place you are. The world is like real Earth, but empty (until the players start to arrive) and only the natural wold (as humanity never existed).
The agent narrates the sheet and can write what you confirm in a sort of lore book, typed events and fixed templates, so the model cannot become the source of truth. I added some NPCs that, i hope, bring some interesting emergent behaviour. Within the game there are also "journeys", which is more like traditional text adventures of trying to find something and bringing it home.
The world is one Rust process and one RocksDB. The Earth is 233,280,000 parcels of one arcminute. Geography is a memory-mapped atlas of about 1.9 GB, built from public natural-state data. Light, weather, and tide are a function of that atlas, the coordinates, and the clock. The world game runs the real time clock.
I would love to have some beta testers for it.