On Steam, you can play Subnautica for free until April 6th

The promotion is timed to the upcoming release of Subnautica 2, which is expected in May.

Subnautica on Steam

Descend into the depths of an alien underwater world filled with wonder and peril. Craft equipment, pilot submarines and out-smart wildlife to explore lush coral reefs, volcanoes, cave systems, and more - all while trying to survive.

store.steampowered.com