Dave the Diver
Dive the Blue Hole together: both divers see each other in the same sea, share the fish and catches, the story and dialogue, day and night and the sushi bar. The host's campaign is shared with the friend. Originally made by S1ii, maintained by Multiplayer Everything. Known issues: real two-account Steam play is not tested yet, diver oxygen and weapons are not synced, clients cannot damage bosses, and some sushi-night cases are open.