Games like JJJ
Games like JJJ include Outlast, Amanda the Adventurer 2, Amanda the Adventurer, Dagon: by H. P. Lovecraft, and PEAK. We matched them by the tags players give JJJ on Steam (Adventure, Interactive Fiction, Mystery Dungeon, Hidden Object, and Choose Your Own Adventure): closest matches first, and among equally close ones the better-known games.

Outlast
Shared: First-Person · Adventure · Atmospheric

Amanda the Adventurer 2
Shared: Adventure · Interactive Fiction · Choose Your Own Adventure

Amanda the Adventurer
Shared: First-Person · Adventure · Interactive Fiction

Dagon: by H. P. Lovecraft
Shared: Interactive Fiction · First-Person · Atmospheric

PEAK
Shared: Adventure · First-Person · 3D

MiSide
Shared: 3D · First-Person · Adventure

IMMORTALITY
Shared: Hidden Object · Choose Your Own Adventure · Interactive Fiction

The Room Two
Shared: Adventure · Hidden Object · Atmospheric

Road 96
Shared: Adventure · First-Person · Choose Your Own Adventure

The Room
Shared: Adventure · Hidden Object · Atmospheric

Five Nights at Freddy's: Secret of the Mimic
Shared: Adventure · First-Person · 3D

Poppy Playtime
Shared: First-Person · Adventure · Horror

The Room Three
Shared: Adventure · Hidden Object · Atmospheric

No Sleep For Kaname Date - From AI: THE SOMNIUM FILES
Shared: Adventure · Interactive Fiction · Choose Your Own Adventure

Nobody Wants to Die
Shared: 3D · Noir · Interactive Fiction

Firewatch
Shared: Adventure · First-Person · Atmospheric

Inside the Backrooms
Shared: Adventure · First-Person · 3D

Layers of Fear (2016)
Shared: Adventure · First-Person · Atmospheric

Killer Frequency
Shared: Adventure · Interactive Fiction · First-Person

Amanda the Adventurer 3
Shared: Adventure · Interactive Fiction · Choose Your Own Adventure

Little Nightmares
Shared: Adventure · Atmospheric · Dark

Escape the Backrooms
Shared: Adventure · First-Person · 3D

Blair Witch
Shared: Adventure · First-Person · Indie

Amnesia: A Machine For Pigs
Shared: Interactive Fiction · First-Person · Adventure