Subnautica is an open world, underwater exploration and adventure game currently under construction at Unknown Worlds, the independent developer behind Natural Selection 2.  
After crash landing on an alien ocean world, the only way to go is down. Subnautica's oceans range from sun drenched shallow coral reefs to treacherous deep-sea trenches. Manage your oxygen supply as you explore Kelp Forests, plateaus, reefs, and winding cave systems. The water teems with life: Some of it helpful, much of it harmful.

Minimal requirements:

Processor: Intel Haswell 2 cores / 4 threads @ 2.5Ghz or equivalent

Graphics: Intel HD 4600 or equivalent

Memory: 4 GB RAM

Disk space: 20 GB available space

System: Windows Vista SP2 or newer, 64-bit