Games like Project X
Games like Project X include Poppy Playtime, Portal 2, Portal, SchoolBoy Runaway, and Bendy and the Ink Machine. We matched them by the tags players give Project X on Steam (3D Platformer, Adventure, Puzzle, 3D, and First-Person): closest matches first, and among equally close ones the better-known games.

Poppy Playtime
Shared: Puzzle · Horror · First-Person

Portal 2
Shared: Puzzle · First-Person · Singleplayer

Portal
Shared: Puzzle · 3D Platformer · First-Person

SchoolBoy Runaway
Shared: Adventure · Puzzle · Horror

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

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

Granny
Shared: Horror · Puzzle · First-Person

A Story About My Uncle
Shared: Adventure · First-Person · 3D Platformer

MiSide
Shared: First-Person · Horror · 3D

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

The Last Campfire
Shared: Adventure · Puzzle · Singleplayer

Little Nightmares II
Shared: Adventure · Puzzle · Horror

Bendy and the Dark Revival
Shared: Horror · First-Person · Adventure

Hello Neighbor
Shared: Horror · First-Person · 3D Platformer

Little Nightmares
Shared: Adventure · Horror · Puzzle

The Room
Shared: Puzzle · Adventure · Singleplayer

Hello Neighbor: Hide and Seek
Shared: Adventure · Horror · Puzzle

The Room 4: Old Sins
Shared: Puzzle · Adventure · Singleplayer

Buckshot Roulette
Shared: First-Person · Horror · 3D

Inside the Backrooms
Shared: Puzzle · Horror · Adventure

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

Hello Neighbor 2
Shared: Adventure · Puzzle · First-Person

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

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