Games like Fluid Simulator
Games like Fluid Simulator include People Playground, BeamNG.drive, Garry's Mod, Brick Rigs, and Besiege. We matched them by the tags players give Fluid Simulator on Steam (Simulation, 2D, Sandbox, Singleplayer, and Physics): closest matches first, and among equally close ones the better-known games.

People Playground
Shared: Sandbox · Physics · 2D

BeamNG.drive
Shared: Simulation · Physics · Sandbox

Garry's Mod
Shared: Sandbox · Physics · Building

Brick Rigs
Shared: Sandbox · Destruction · Simulation

Besiege
Shared: Simulation · Sandbox · Physics

Space Engineers
Shared: Sandbox · Simulation · Building

Kerbal Space Program
Shared: Simulation · Sandbox · Physics

Hardspace: Shipbreaker
Shared: Simulation · Singleplayer · Physics

Universe Sandbox
Shared: Simulation · Sandbox · Physics

WorldBox - God Simulator
Shared: Simulation · Sandbox · Destruction

Teardown
Shared: Sandbox · Physics · Destruction

Spaceflight Simulator
Shared: Sandbox · Simulation · 2D

Cities: Skylines II
Shared: Simulation · Sandbox · Singleplayer

Planet Coaster
Shared: Simulation · Sandbox · Building

Prison Architect
Shared: Simulation · Sandbox · Building

Totally Accurate Battle Simulator
Shared: Simulation · Sandbox · Physics

Sand:box
Shared: Simulation · Sandbox · 2D

Poly Bridge
Shared: Simulation · Physics · Singleplayer

House Flipper
Shared: Simulation · Singleplayer · Sandbox

Goat Simulator
Shared: Simulation · Sandbox · Physics

Cities: Skylines
Shared: Simulation · Sandbox · Singleplayer

Bridge Constructor Portal
Shared: Simulation · Physics · 2D

Medieval Engineers
Shared: Sandbox · Physics · Simulation

The Sims™ 4
Shared: Simulation · Singleplayer · Sandbox