Games like Ark Defender
Games like Ark Defender include FTL: Faster Than Light, Dome Keeper, BALL x PIT, Oxygen Not Included, and Heat Signature. We matched them by the tags players give Ark Defender on Steam (Roguelike, Resource Management, Space Sim, 2D, and Sci-fi): closest matches first, and among equally close ones the better-known games.

FTL: Faster Than Light
Shared: Roguelike · Sci-fi · Perma Death

Dome Keeper
Shared: Roguelike · Resource Management · Sci-fi

BALL x PIT
Shared: Roguelike · Action · 2D

Oxygen Not Included
Shared: Resource Management · 2D · Singleplayer

Heat Signature
Shared: Roguelike · Top-Down · Sci-fi

Cosmoteer: Starship Architect & Commander
Shared: Sci-fi · 2D · Space Sim

Brotato
Shared: Roguelike · Singleplayer · Sci-fi

Vampire Survivors
Shared: 2D · Roguelike · Singleplayer

Door Kickers
Shared: Simulation · Top-Down · 2D

Dyson Sphere Program
Shared: Resource Management · Sci-fi · Simulation

Noita
Shared: Roguelike · 2D · Perma Death

Elite Dangerous
Shared: Space Sim · Sci-fi · Simulation

Endless Sky
Shared: Sci-fi · 2D · Simulation

Skul: The Hero Slayer
Shared: Roguelike · 2D · Action

Battlevoid: Harbinger
Shared: Roguelike · Simulation · 2D

Halo: Spartan Assault
Shared: Sci-fi · Action · Top-Down

Trigon: Space Story
Shared: Roguelike · Resource Management · Singleplayer

The Escapists
Shared: 2D · Simulation · Singleplayer

The Binding of Isaac
Shared: Roguelike · Top-Down · Indie

Maniac
Shared: Roguelike · Simulation · Singleplayer

X Rebirth
Shared: Space Sim · Sci-fi · Simulation

Nubby's Number Factory
Shared: Roguelike · Singleplayer · 2D

Dungeon of the ENDLESS™
Shared: Roguelike · Sci-fi · Strategy

Nuclear Throne
Shared: Roguelike · Action · Indie