Games like World of Contraptions
Games like World of Contraptions include Kerbal Space Program, Garry's Mod, People Playground, Poly Bridge, and Besiege. We matched them by the tags players give World of Contraptions on Steam (Building, Physics, Sandbox, Robots, and Simulation): closest matches first, and among equally close ones the better-known games.

Kerbal Space Program
Shared: Sandbox · Physics · Simulation

Garry's Mod
Shared: Sandbox · Physics · Building

People Playground
Shared: Sandbox · Physics · Singleplayer

Poly Bridge
Shared: Building · Physics · Simulation

Besiege
Shared: Physics · Sandbox · Simulation

BeamNG.drive
Shared: Physics · Simulation · Sandbox

Brick Rigs
Shared: Building · Sandbox · Physics

Totally Accurate Battle Simulator
Shared: Sandbox · Simulation · Physics

Teardown
Shared: Physics · Sandbox · Destruction

Poly Bridge 2
Shared: Building · Physics · Simulation

Space Engineers
Shared: Building · Sandbox · Physics

Cities: Skylines
Shared: Building · Simulation · Sandbox

Hardspace: Shipbreaker
Shared: Physics · Simulation · Sandbox

Goat Simulator
Shared: Simulation · Sandbox · Physics

Kerbal Space Program 2
Shared: Sandbox · Building · Physics

Bridge Constructor Portal
Shared: Physics · Building · Simulation

Aviassembly
Shared: Building · Physics · Sandbox

Fun with Ragdolls: The Game
Shared: Physics · Sandbox · Building

Crazy Machines 3
Shared: Physics · Simulation · Sandbox

while True: learn()
Shared: Simulation · Building · Sandbox

Scrap Mechanic
Shared: Building · Sandbox · Physics

Two Point Hospital
Shared: Building · Simulation · Sandbox

Planet Coaster
Shared: Building · Simulation · Sandbox

Car Mechanic Simulator 2018
Shared: Building · Simulation · Singleplayer