Games like Planet Game
Games like Planet Game include Portal, Defy Gravity Extended, Portal 2, Zup!, and Zup! F. We matched them by the tags players give Planet Game on Steam (Casual, Puzzle, Puzzle Platformer, 3D, and Space): closest matches first, and among equally close ones the better-known games.

Portal
Shared: Puzzle · Puzzle Platformer · Singleplayer

Defy Gravity Extended
Shared: Puzzle Platformer · Puzzle · Space

Portal 2
Shared: Puzzle · Singleplayer · Puzzle Platformer

Zup!
Shared: Casual · Puzzle · Physics

Zup! F
Shared: Casual · Puzzle · Physics

Human Fall Flat
Shared: Puzzle · Physics · Puzzle Platformer

Zup! S
Shared: Casual · Puzzle · Physics

Zup! 2
Shared: Casual · Puzzle · Physics

Zup! X
Shared: Casual · Puzzle · Physics

Peggle Deluxe
Shared: Casual · Puzzle · Singleplayer

Donut County
Shared: Casual · Puzzle · Physics

Zup! 3
Shared: Casual · Puzzle · Physics

Monument Valley
Shared: Puzzle · Casual · Singleplayer

Zup! 8
Shared: Casual · Puzzle · Physics

COCOON
Shared: Puzzle · Puzzle Platformer · 3D

Viewfinder
Shared: Puzzle · Puzzle Platformer · Singleplayer

Moncage
Shared: Casual · Puzzle · Singleplayer

Zup! Z
Shared: Puzzle · Casual · Physics

Quantum Conundrum
Shared: Puzzle · Puzzle Platformer · Casual

LIMBO
Shared: Puzzle Platformer · Puzzle · Singleplayer

Zup! 5
Shared: Casual · Puzzle · Physics

Trine 2: Complete Story
Shared: Puzzle Platformer · Puzzle · Casual

Hardspace: Shipbreaker
Shared: Space · Physics · Puzzle

Zup! 6
Shared: Casual · Puzzle · Physics