Games like Not Alone
Games like Not Alone include Poppy Playtime, Outlast, MiSide, Garten of Banban, and Phasmophobia. We matched them by the tags players give Not Alone on Steam (Horror, Psychological Horror, First-Person, Singleplayer, and 3D): closest matches first, and among equally close ones the better-known games.

Poppy Playtime
Shared: Horror · Singleplayer · First-Person

Outlast
Shared: Horror · First-Person · Psychological Horror

MiSide
Shared: Psychological Horror · Horror · First-Person

Garten of Banban
Shared: Horror · First-Person · Psychological Horror

Phasmophobia
Shared: Horror · Psychological Horror · First-Person

Outlast 2
Shared: Horror · Psychological Horror · First-Person

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

Buckshot Roulette
Shared: Horror · First-Person · Dark

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

SOMA
Shared: Horror · Psychological Horror · Atmospheric

Five Nights at Freddy's
Shared: Horror · Singleplayer · Psychological Horror

Visage
Shared: Horror · Psychological Horror · First-Person

From The Darkness
Shared: Horror · Psychological Horror · First-Person

Five Nights at Freddy's 2
Shared: Horror · Singleplayer · Psychological Horror

Little Nightmares
Shared: Horror · Singleplayer · Atmospheric

Subliminal
Shared: Psychological Horror · Singleplayer · Horror

Sally Face - Episode One
Shared: Psychological Horror · Horror · Dark

Little Nightmares II
Shared: Horror · Singleplayer · Psychological Horror

Garten of Banban 2
Shared: Horror · First-Person · Singleplayer

Bendy and the Ink Machine
Shared: Horror · First-Person · Singleplayer

The Mortuary Assistant
Shared: Horror · Singleplayer · Atmospheric

Mouthwashing
Shared: Horror · Psychological Horror · Atmospheric

Ready or Not
Shared: Horror · Singleplayer · Realistic

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