Games like Modbox
Games like Modbox include Garry's Mod, BeamNG.drive, Space Engineers, Scrap Mechanic, and CarX Drift Racing Online. We matched them by the tags players give Modbox on Steam (Moddable, Sandbox, Physics, Multiplayer, and Programming): closest matches first, and among equally close ones the better-known games.

Garry's Mod
Shared: Moddable · Sandbox · Physics

BeamNG.drive
Shared: Physics · Simulation · Sandbox

Space Engineers
Shared: Sandbox · Physics · Simulation

Scrap Mechanic
Shared: Sandbox · Multiplayer · Physics

CarX Drift Racing Online
Shared: Moddable · Multiplayer · Sandbox

People Playground
Shared: Sandbox · Physics · Moddable

Kerbal Space Program
Shared: Sandbox · Physics · Simulation

Brick Rigs
Shared: Sandbox · Multiplayer · Physics

Besiege
Shared: Sandbox · Physics · Moddable

Wobbly Life
Shared: Sandbox · Multiplayer · Simulation

Blade and Sorcery
Shared: Moddable · Sandbox · VR

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

Teardown
Shared: Sandbox · Physics · Multiplayer

Hot Dogs, Horseshoes & Hand Grenades
Shared: Sandbox · Physics · VR

Assetto Corsa
Shared: Multiplayer · Simulation · VR

BONEWORKS
Shared: Physics · Sandbox · VR

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

House Flipper
Shared: Multiplayer · Simulation · Sandbox

Tabletop Simulator
Shared: Sandbox · Multiplayer · Simulation

Rust
Shared: Multiplayer · Sandbox · Open World

X-Plane 11
Shared: Simulation · Multiplayer · Physics

Fireworks Mania - An Explosive Simulator
Shared: Sandbox · Multiplayer · Physics

Grand Theft Auto V Legacy
Shared: Multiplayer · Open World · Action

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