Games like Rain Ruin
Games like Rain Ruin include Five Nights at Freddy's: Security Breach, Firewatch, Escape the Backrooms, The Exit 8, and September 7th. We matched them by the tags players give Rain Ruin on Steam (Horror, Adventure, 3D, 3D Platformer, and Realistic): closest matches first, and among equally close ones the better-known games.

Five Nights at Freddy's: Security Breach
Shared: Horror · First-Person · 3D

Firewatch
Shared: Adventure · Walking Simulator · First-Person

Escape the Backrooms
Shared: Horror · First-Person · Adventure

The Exit 8
Shared: Horror · Exploration · Walking Simulator

September 7th
Shared: Horror · 3D Platformer · 3D

The Forest
Shared: Horror · Adventure · First-Person

Five Nights at Freddy's: Secret of the Mimic
Shared: Horror · Adventure · First-Person

Scanner Sombre
Shared: Horror · Adventure · Walking Simulator

PEAK
Shared: Adventure · 3D · First-Person

Layers of Fear (2016)
Shared: Horror · First-Person · Walking Simulator

Ready or Not
Shared: Realistic · Horror · First-Person

Valley
Shared: Adventure · First-Person · Exploration

What Remains of Edith Finch
Shared: Adventure · Walking Simulator · First-Person

Platform 8
Shared: Adventure · Walking Simulator · 3D

The Beast Inside
Shared: Horror · Adventure · First-Person

The Death | Thần Trùng
Shared: Horror · Adventure · Realistic

Kona
Shared: Adventure · First-Person · Walking Simulator

Visage
Shared: Horror · Adventure · First-Person

Lethal Company
Shared: Horror · First-Person · Exploration

Metel - Horror Escape
Shared: Horror · 3D · First-Person

Subnautica
Shared: Horror · Adventure · Exploration

Amenti
Shared: Horror · Adventure · 3D

MiSide
Shared: Horror · 3D · First-Person

Fears to Fathom® - Scratch Creek
Shared: Horror · Adventure · First-Person