Games like Concept 20
Games like Concept 20 include Portal 2, LIMBO, Gunpoint, BEEP, and FEZ. We matched them by the tags players give Concept 20 on Steam (Indie, Strategy, Singleplayer, Platformer, and Puzzle): closest matches first, and among equally close ones the better-known games.

Portal 2
Shared: Singleplayer · Platformer · Puzzle

LIMBO
Shared: Indie · Platformer · Puzzle

Gunpoint
Shared: Indie · Puzzle · Singleplayer

BEEP
Shared: Indie · Platformer · Singleplayer

FEZ
Shared: Indie · Platformer · Puzzle

Mini Metro
Shared: Strategy · Puzzle · Indie

Polarity
Shared: Indie · Puzzle · Singleplayer

The Basement Collection
Shared: Indie · Strategy · Platformer

Papers, Please
Shared: Indie · Singleplayer · Puzzle

Plague Inc: Evolved
Shared: Strategy · Indie · Singleplayer

Mini Motorways
Shared: Strategy · Indie · Puzzle

Hollow Knight
Shared: Platformer · Indie · Singleplayer

Seen
Shared: Indie · Singleplayer · Puzzle

ISLANDERS
Shared: Strategy · Indie · Puzzle

Braid
Shared: Indie · Puzzle · Platformer

Baba Is You
Shared: Indie · Puzzle · Singleplayer

Buckshot Roulette
Shared: Strategy · Indie · Singleplayer

Into the Breach
Shared: Strategy · Indie · Puzzle

Hollow Knight: Silksong
Shared: Indie · Singleplayer · Platformer

Defy Gravity Extended
Shared: Indie · Platformer · Puzzle

Hexcells
Shared: Indie · Puzzle · Singleplayer

The Legend of Bum-Bo
Shared: Indie · Strategy · Singleplayer

The Escapists
Shared: Strategy · Singleplayer · Indie

Zup! S
Shared: Indie · Puzzle · Singleplayer