SimPolis is an in-development videogame in which players are custodians of a virtual world inspired by the concept of a Miniature Village. The game uses an innovative technology standard which allows players to create and publish anything, shared with the world on a federation of servers; in short, it’s a game that we build together. More than this, the federated game data is free and open-source, owned in common, and the ambition is that the game itself is the creation of its player base: this is a Games Commons. This is all we’ll say about the concept for now, but it has a lot of interesting implications.