Games like X2: The Threat
Games like X2: The Threat include X4: Foundations, Elite Dangerous, X Rebirth, Stellaris, and X3: Terran Conflict. We matched them by the tags players give X2: The Threat on Steam (Space, Strategy, Simulation, Sci-fi, and Singleplayer): closest matches first, and among equally close ones the better-known games.

X4: Foundations
Shared: Space · Simulation · Open World

Elite Dangerous
Shared: Space · Sci-fi · Simulation

X Rebirth
Shared: Space · Simulation · Sci-fi

Stellaris
Shared: Space · Strategy · Sci-fi

X3: Terran Conflict
Shared: Space · Simulation · Strategy

Kerbal Space Program
Shared: Space · Simulation · Sandbox

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

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

EVE Online
Shared: Space · Open World · Space Sim

SPORE™ Galactic Adventures
Shared: Space · Simulation · Strategy

Endless Sky
Shared: Space · Sci-fi · Simulation

Dyson Sphere Program
Shared: Space · Simulation · Open World

Starpoint Gemini Warlords
Shared: Space · Strategy · Simulation

Starfield
Shared: Space · Singleplayer · Open World

X3: Reunion
Shared: Space · Strategy · Simulation

SPORE™
Shared: Simulation · Open World · Space

Rebel Galaxy
Shared: Space · Sci-fi · Open World

Avorion
Shared: Space · Sandbox · Space Sim

Jurassic World Evolution
Shared: Simulation · Strategy · Singleplayer

Space Engineers
Shared: Space · Simulation · Sandbox

Starminer
Shared: Space · Sci-fi · Economy

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

SpaceEngine
Shared: Sci-fi · Space · Open World

Empyrion - Galactic Survival
Shared: Space · Simulation · Open World