A wildly new ambitious MMO called SEED sees the entire player base touch down on a freshly-colonized planet, build a couple Seedlings who aren't too far off your typical The Sims characters, and collaborate to "build real, functional societies" that run even when you're not looking.
"SEED is a persistent, player-driven life and MMO simulation," developer Klang's website explains. But the nitty gritty details are what make SEED seem really exciting. You essentially build autonomous characters, each with their own personalities who will go about their routines whether you log in or not. Before long, they'll have built up societies that mirror our real life, only this time on a faraway planet. It's basically Rimworld but it's always online and borrows from The Sims.