In RimWorld, you play as crash-landed survivors who have to eke out a new existence on a hostile planet, surviving and perhaps thriving between raider attacks, AI uprisings, and swarms of hostile insects. The game has a handful of expansions with new events, and the latest, Anomaly, is the scariest one yet. If you only have the spare scratch to pick up one RimWorld expansion, Anomaly is by far your best choice.