Games like Zombie Siege
Games like Zombie Siege include Plants vs. Zombies GOTY Edition, They Are Billions, Tower Dominion, Emberward, and Necrosmith. We matched them by the tags players give Zombie Siege on Steam (Tower Defense, Roguelite, Loot, Strategy, and Zombies): closest matches first, and among equally close ones the better-known games.

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

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

Tower Dominion
Shared: Tower Defense · Strategy · Base Building

Emberward
Shared: Tower Defense · Roguelite · Strategy

Necrosmith
Shared: Tower Defense · Roguelite · Zombies

Mindustry
Shared: Tower Defense · Base Building · Strategy

The King is Watching
Shared: Tower Defense · Base Building · Strategy

Kingdom Rush - Tower Defense
Shared: Tower Defense · Strategy · Tactical

Nordhold
Shared: Tower Defense · Roguelite · Strategy

Creeper World 3: Arc Eternal
Shared: Tower Defense · Strategy · Base Building

GemCraft - Chasing Shadows
Shared: Tower Defense · Strategy · Top-Down

Bloons TD 6
Shared: Tower Defense · Strategy · Singleplayer

Oxygen Not Included
Shared: Base Building · Resource Management · Strategy

Dungeon Warfare
Shared: Tower Defense · Strategy · 2D

Sir, We Have an Orc Problem
Shared: Tower Defense · Roguelite · Strategy

Drill Core
Shared: Roguelite · Tower Defense · Strategy

Plague Inc: Evolved
Shared: Strategy · Zombies · Tactical

Grim Nights
Shared: Tower Defense · Strategy · Base Building

Minimalist Tower Defense
Shared: Tower Defense · Strategy · Base Building

Kingdom Rush Origins - Tower Defense
Shared: Tower Defense · Strategy · 2D

Diplomacy is Not an Option
Shared: Resource Management · Zombies · Base Building

Loop Hero
Shared: Roguelite · Tactical · Resource Management

Factorio
Shared: Base Building · Strategy · Resource Management

Heretic's Fork
Shared: Tower Defense · Strategy · Roguelite

