Games like GRANDFATHER
Games like GRANDFATHER include MiSide, Mouthwashing, Fears to Fathom - Ironbark Lookout, No, I'm not a Human, and Layers of Fear (2016). We matched them by the tags players give GRANDFATHER on Steam (Horror, Psychological Horror, Realistic, Atmospheric, and Singleplayer): closest matches first, and among equally close ones the better-known games.

MiSide
Shared: Psychological Horror · Horror · Story Rich

Mouthwashing
Shared: Horror · Psychological Horror · Atmospheric

Fears to Fathom - Ironbark Lookout
Shared: Horror · Psychological Horror · Atmospheric

No, I'm not a Human
Shared: Horror · Psychological Horror · Singleplayer

Layers of Fear (2016)
Shared: Horror · Psychological Horror · Atmospheric

SOMA
Shared: Horror · Psychological Horror · Atmospheric

Firewatch
Shared: Atmospheric · Story Rich · Singleplayer

SILENT HILL 2
Shared: Horror · Psychological Horror · Atmospheric

Summer of '58
Shared: Horror · Psychological Horror · Atmospheric

Outlast
Shared: Horror · Psychological Horror · Atmospheric

What Remains of Edith Finch
Shared: Atmospheric · Story Rich · First-Person

Subliminal
Shared: Psychological Horror · Realistic · Atmospheric

Still Wakes the Deep
Shared: Horror · Psychological Horror · First-Person

Amnesia: A Machine For Pigs
Shared: Horror · Atmospheric · Psychological Horror

Poppy Playtime
Shared: Horror · Singleplayer · Psychological Horror

Resident Evil 7 Biohazard
Shared: Horror · Singleplayer · First-Person

Visage
Shared: Horror · Psychological Horror · Singleplayer

Outlast 2
Shared: Horror · Psychological Horror · Singleplayer

The Park®
Shared: Horror · Psychological Horror · Singleplayer

Backrooms: Escape Together
Shared: Horror · Psychological Horror · Atmospheric

Ready or Not
Shared: Realistic · Horror · Singleplayer

Little Nightmares II
Shared: Horror · Singleplayer · Psychological Horror

KARMA: The Dark World
Shared: Psychological Horror · Horror · Atmospheric

Garten of Banban
Shared: Horror · Psychological Horror · Singleplayer