Games like Astral Guardian
Games like Astral Guardian include Bloons TD 6, Plants vs. Zombies GOTY Edition, Rogue Tower, The Riftbreaker, and Legion TD 2 - Multiplayer Tower Defense. We matched them by the tags players give Astral Guardian on Steam (Casual, Strategy, Tower Defense, Real Time Tactics, and 3D): closest matches first, and among equally close ones the better-known games.

Bloons TD 6
Shared: Strategy · Tower Defense · Casual

Plants vs. Zombies GOTY Edition
Shared: Tower Defense · Strategy · Casual

Rogue Tower
Shared: Strategy · Tower Defense · Casual

The Riftbreaker
Shared: Tower Defense · Base Building · Survival

Legion TD 2 - Multiplayer Tower Defense
Shared: Tower Defense · Strategy · Casual

Kingdom Two Crowns
Shared: Tower Defense · Building · Strategy

They Are Billions
Shared: Strategy · Base Building · Tower Defense

7 Days to Die
Shared: Survival · Base Building · Building

Castle Story
Shared: Strategy · Building · Tower Defense

Dungeon Defenders
Shared: Tower Defense · Strategy · Survival

Factorio
Shared: Strategy · Base Building · Survival

Liars Bar
Shared: Casual · 3D · PvP

Creeper World 4
Shared: Tower Defense · Real Time Tactics · Strategy

Planetary Annihilation: TITANS
Shared: Strategy · Real Time Tactics · Base Building

Mindustry
Shared: Tower Defense · Strategy · Base Building

Oxygen Not Included
Shared: Survival · Base Building · Building

Raft
Shared: Survival · Building · Base Building

Minimalist Tower Defense
Shared: Strategy · Tower Defense · Real Time Tactics

Thronefall
Shared: Strategy · Tower Defense · Building

Bloons TD 5
Shared: Strategy · Tower Defense · Casual

Plague Inc: Evolved
Shared: Strategy · Casual · Indie

Ninja Kiwi Archive
Shared: Casual · Strategy · Tower Defense

PUBG: BATTLEGROUNDS
Shared: Survival · Strategy · PvP

Bee Island
Shared: Strategy · Tower Defense · Building