Games like X: Tension
Games like X: Tension include X4: Foundations, X Rebirth, Elite Dangerous, Kerbal Space Program, and Stellaris. We matched them by the tags players give X: Tension on Steam (Simulation, Strategy, Space, Sci-fi, and Space Sim): closest matches first, and among equally close ones the better-known games.

X4: Foundations
Shared: Simulation · Space · Space Sim

X Rebirth
Shared: Simulation · Space · Sci-fi

Elite Dangerous
Shared: Space · Space Sim · Simulation

Kerbal Space Program
Shared: Simulation · Space · Sandbox

Stellaris
Shared: Strategy · Space · Sci-fi

X3: Terran Conflict
Shared: Simulation · Space · Strategy

Hardspace: Shipbreaker
Shared: Simulation · Space · Sci-fi

Dyson Sphere Program
Shared: Space · Simulation · Sci-fi

Starpoint Gemini Warlords
Shared: Space · Strategy · Simulation

Jurassic World Evolution
Shared: Simulation · Strategy · Sandbox

SPORE™ Galactic Adventures
Shared: Simulation · Space · Strategy

No Man's Sky
Shared: Space · Sci-fi · Open World

Space Engineers
Shared: Space · Simulation · Sandbox

X3: Reunion
Shared: Simulation · Space · Strategy

Jurassic World Evolution 2
Shared: Simulation · Strategy · Sandbox

SpaceEngine
Shared: Sci-fi · Space · Sandbox

FTL: Faster Than Light
Shared: Strategy · Space · Sci-fi

Mount & Blade II: Bannerlord
Shared: Strategy · Sandbox · Simulation

Endless Sky
Shared: Space · Simulation · Sci-fi

SPORE™
Shared: Simulation · Sandbox · Space

Avorion
Shared: Sandbox · Space · Space Sim

Rebel Galaxy
Shared: Space · Sci-fi · Simulation

Cities: Skylines
Shared: Simulation · Strategy · Sandbox

STAR WARS™: Squadrons
Shared: Space · Simulation · Sci-fi