Endless, Endless Ocean is an Open World, Procedurally Generated, Survival game set in an ocean enviroment (duh).
The Ocean
In order to SURVIVE you'll need to salvage every resource at your disposal. No one's gonna hold your hand here, explore the ocean to learn new stuff useful for your survival.
Remember that everything is against you here, but you will adapt, with that the challenges for you will change too. Danger will be always present.
A Forever Sandbox
Choose either story mode, or endless survival. At disposal you have various sandbox settings to adjust the game to whatever you want it to be.