Subnautica is a survival, adventure game set in an open world environment and played from a first-person perspective. The player controls the lone survivor of a crashed space ship, on an aquatic planet. The main objective of the player is to explore the game's world and survive the dangers of the planet while at the same time following the story of the game. Subnautica allows the player to collect resources, construct tools, bases, and submersibles, and interact with the planet's wildlife. The game includes four play modes: "Survival", in which the player needs to ensure a steady supply of food, water, and oxygen; "Freedom", in which hunger and thirst are disabled; "Hardcore", which is the same as Survival, except that if the player dies, the player will no longer be able to respawn; and "Creative", in which the hunger, thirst, health, and oxygen features are all disabled, all the crafting blueprints are acquired, no resources are needed to craft and the submersibles do not need energy and cannot be damaged. The game is mainly set underwater, with two explorable islands.
The game was released as early access in 2014, and the official release happened in January 2018.
Source: Wikipedia, "Subnautica", available under the CC-BY-SA License.