Games like Once Upon The Universe
Games like Once Upon The Universe include Kerbal Space Program, WorldBox - God Simulator, Universe Sandbox, X4: Foundations, and Stellaris. We matched them by the tags players give Once Upon The Universe on Steam (God Game, Space Sim, Sandbox, Life Sim, and Space): closest matches first, and among equally close ones the better-known games.
Kerbal Space Program
Shared: Sandbox · Space · Space Sim
WorldBox - God Simulator
Shared: God Game · Sandbox · Simulation
Universe Sandbox
Shared: Sandbox · Space Sim · Space
X4: Foundations
Shared: Space Sim · Space · Sandbox
Stellaris
Shared: Space · Strategy · Sandbox
Hardspace: Shipbreaker
Shared: Space · Sandbox · Simulation
SPORE™
Shared: God Game · Sandbox · Space
Stardew Valley
Shared: Life Sim · Pixel Graphics · Sandbox
FTL: Faster Than Light
Shared: Space · Strategy · Sci-fi
Elite Dangerous
Shared: Space Sim · Space · Simulation
Dyson Sphere Program
Shared: Space · Sandbox · Simulation
Spaceflight Simulator
Shared: Space Sim · Sandbox · Space
X Rebirth
Shared: Space Sim · Space · Simulation
Space Engineers
Shared: Sandbox · Space · Simulation
Cosmoteer: Starship Architect & Commander
Shared: Space · Space Sim · Sci-fi
X3: Terran Conflict
Shared: Sandbox · Space · Space Sim
Totally Accurate Battle Simulator
Shared: Sandbox · Simulation · Strategy
Universe Sandbox
Shared: Sandbox · Space · Simulation
Starpoint Gemini Warlords
Shared: Space · Space Sim · Strategy
SpaceEngine
Shared: Sandbox · Space Sim · Space
Kerbal Space Program 2
Shared: Sandbox · Space · Space Sim
Reus
Shared: God Game · Strategy · Sandbox
The Universim
Shared: God Game · Sandbox · Space
SPORE™ Galactic Adventures
Shared: Space · Simulation · Sandbox