Games like Gamebox
Games like Gamebox include Garry's Mod, Don't Starve, People Playground, Mount & Blade II: Bannerlord, and Teardown. We matched them by the tags players give Gamebox on Steam (Indie, Sandbox, Moddable, Singleplayer, and Multiplayer): closest matches first, and among equally close ones the better-known games.

Garry's Mod
Shared: Sandbox · Moddable · Multiplayer

Don't Starve
Shared: Indie · Sandbox · Singleplayer

People Playground
Shared: Sandbox · Moddable · Singleplayer

Mount & Blade II: Bannerlord
Shared: Sandbox · Multiplayer · Singleplayer

Teardown
Shared: Sandbox · Indie · Multiplayer

Space Engineers
Shared: Sandbox · Multiplayer · Singleplayer

Terraria
Shared: Sandbox · Multiplayer · Indie

Ravenfield
Shared: Singleplayer · Sandbox · Moddable

Feed and Grow: Fish
Shared: Multiplayer · Indie · Early Access

BeamNG.drive
Shared: Sandbox · Moddable · Multiplayer

Kerbal Space Program
Shared: Sandbox · Moddable · Indie

Mount & Blade: Warband
Shared: Sandbox · Multiplayer · Moddable

Stardew Valley
Shared: Multiplayer · Sandbox · Indie

Rusted Warfare - RTS
Shared: Moddable · Indie · Multiplayer

Easy Red 2
Shared: Sandbox · Moddable · Singleplayer

Scrap Mechanic
Shared: Sandbox · Multiplayer · Singleplayer

Beat Saber
Shared: Moddable · Multiplayer · Singleplayer

House Flipper
Shared: Singleplayer · Multiplayer · Sandbox

Blockland
Shared: Sandbox · Indie · Multiplayer

Project Zomboid
Shared: Sandbox · Multiplayer · Indie

Game Dev Tycoon
Shared: Indie · Singleplayer · Moddable

Besiege
Shared: Sandbox · Moddable · Multiplayer

RimWorld
Shared: Sandbox · Singleplayer · Moddable

Grand Theft Auto IV: The Complete Edition
Shared: Multiplayer · Singleplayer · Moddable