Games like Ostranauts
Games like Ostranauts include EVE Online, Kerbal Space Program, X4: Foundations, No Man's Sky, and Elite Dangerous. We matched them by the tags players give Ostranauts on Steam (Flight, Simulation, Space Sim, Sandbox, and Difficult): closest matches first, and among equally close ones the better-known games.
EVE Online
Shared: Space Sim · Simulation · Difficult
Kerbal Space Program
Shared: Simulation · Sandbox · Space
X4: Foundations
Shared: Simulation · Space Sim · Space
No Man's Sky
Shared: Space · Survival · Exploration
Elite Dangerous
Shared: Space Sim · Simulation · Space
Space Engineers
Shared: Sandbox · Simulation · Survival
Avorion
Shared: Sandbox · Space Sim · Flight
Empyrion - Galactic Survival
Shared: Simulation · Space · Survival
Kerbal Space Program 2
Shared: Sandbox · Space · Simulation
Kenshi
Shared: Sandbox · Survival · Simulation
Spaceflight Simulator
Shared: Space Sim · Sandbox · Simulation
Universe Sandbox
Shared: Simulation · Sandbox · Space Sim
Starminer
Shared: Space Sim · Sandbox · Space
Don't Starve Together
Shared: Survival · Sandbox · Difficult
Stormworks: Build and Rescue
Shared: Sandbox · Flight · Simulation
SpaceEngine
Shared: Sandbox · Space Sim · Space
SPORE™
Shared: Sandbox · Simulation · Space
FTL: Faster Than Light
Shared: Space · Difficult · Simulation
Core Keeper
Shared: Survival · Sandbox · Exploration
Reentry - A Space Flight Simulator
Shared: Simulation · Flight · Space Sim
Stardew Valley
Shared: Simulation · Sandbox · Life Sim
X Rebirth
Shared: Simulation · Space Sim · Space
The Long Dark
Shared: Survival · Exploration · Simulation
Don't Starve
Shared: Survival · Sandbox · Exploration