Games like Astro Traveler
Games like Astro Traveler include Grand Theft Auto V Legacy, Terraria, Starbound, Crysis Remastered, and Elite Dangerous. We matched them by the tags players give Astro Traveler on Steam (Action, Adventure, Casual, Sandbox, and Shooter): closest matches first, and among equally close ones the better-known games.

Grand Theft Auto V Legacy
Shared: Action · Adventure · Shooter

Terraria
Shared: Sandbox · Adventure · 2D

Starbound
Shared: Sandbox · Adventure · Space

Crysis Remastered
Shared: Action · Shooter · Sandbox

Elite Dangerous
Shared: Space Sim · Action · Adventure

Just Cause 2
Shared: Action · Sandbox · Adventure

Just Cause™ 3
Shared: Action · Adventure · Shooter

No Man's Sky
Shared: Adventure · Sandbox · Space

Red Dead Redemption 2
Shared: Adventure · Action · Shooter

Far Cry 3
Shared: Action · Adventure · Shooter

Wobbly Life
Shared: Adventure · Sandbox · Action

EVE Online
Shared: Adventure · Space Sim · Sandbox

Chorus
Shared: Action · Adventure · Shooter

Fallout 4
Shared: Adventure · Shooter · Action

Grand Theft Auto V Enhanced
Shared: Action · Adventure · Shooter

Grand Theft Auto IV: The Complete Edition
Shared: Action · Adventure · Sandbox

SpaceEngine
Shared: Casual · Sandbox · Space Sim

Just Cause 4 Reloaded
Shared: Action · Adventure · Sandbox

Warhammer 40,000: Space Marine 2
Shared: Action · Adventure · Sci-fi

SPORE™
Shared: Sandbox · Casual · Action

Rebel Galaxy
Shared: Adventure · Action · Space Sim

Cyberhunt
Shared: Action · Casual · Adventure

Half-Life 2
Shared: Action · Adventure · Shooter

Endless Sky
Shared: Adventure · Action · 2D