Barotrauma

Enter a dystopic, futuristic universe where humanity has been forced to flee to Jupiter in order to survive. Jupiter's moon, Europa, is the only suitable place in our solar system, but there is a little inconvenience. the icy surface of Europa can't harbor human life, and human civilization had to find a way to survive in the ocean below. 

Barotrauma is a co-op survival horror game where you play as the crew of a submarine. Cooperate with up to 16 players to explore the surrounding environment and find ways to survive. The game pits you against a procedurally generated world full of perils, where you will have to react to unexpected events. Barotrauma has a crafting system, and you will be able to gather materials and craft everything you need to survive. 

Choose from six different classes, Captain, Engineer, Mechanic, Medic, Security officer, and Assistant. Each one has different abilities that you can expand and improve as you gain experience and progress through the game. But the most important element for your survival is cooperation. You need to choose who to trust. There are several factions, each with its own agenda, and only by supporting the appropriate one do you have a chance of surviving in such a hostile underwater environment.

Barotrauma features detailed graphics in 2D and a unique art style. It supports heavy modding so you can find plenty of different ways to enjoy the game.