Barotrauma

Barotrauma is a 2D co-op submarine simulator set under the ice crust of Europa, in a future where humanity has retreated from the irradiated surface and now lives in the ocean below. You crew a submarine making transit between colonies, and the game is openly inspired by FTL, Rimworld, Dwarf Fortress and Space Station 13 — meaning the threats include monsters in the dark, but also the rest of the crew if a session goes that way.

The ship has working systems, all of which need attention. Sonar, nuclear reactor, weapons, engines, pumps, hull repairs, wiring — none of it runs itself, and the difference between a competent crew and an incompetent one is whether the reactor melts down before the leak is patched. Six player classes — Captain, Engineer, Mechanic, Medic, Security Officer, Assistant — each carry distinct skills and talent trees, and the game is built around explicit specialisation so a single player can't reasonably cover every role on a busy run.

A campaign frames the play around the four factions of Europa, mission-based reputation gains and consequences, procedural mission generation, and a comprehensive crafting and medical system. Up to sixteen players can crew a single sub, with bots filling unused slots. Built-in editors for submarines, characters and procedural animations let the community build new ships and creatures, with Workshop sharing and the game's source openly available on GitHub for deeper modding. Most game data sits in editable XML; the modding community is wide and weird, and a lot of long-running servers run extensively modified rule sets.