The title supports up to 16 players total on one server, but you can set that to a much lower number and even password-protect it so you can be sure it's just your buddies on there with you. There's a new video available that goes through just what to expect from the title in this Early Access phase.

Barotrauma's premise is that in the future (naturally), humans have fled Earth and settled on Jupiter's smallest moon as it's one of a handful of places in the Solar System that has a chance of supporting life. You and up to 15 of your friends can explore the mysterious ocean depths across three different game modes: Sandbox, Mission, and Campaign. Sandbox is just as the name implies; there's no set objective or goal, just work together to pilot a submarine and survive. Mission mode provides you with a specific submarine to control in order to complete a specific set of objectives, and Campaign lets you pick a submarine before you set out to complete as many missions as possible. Levels are all procedurally generated so you'll have a different experience each time you play.