Citadel Zero

Defend the last citadel on a dying alien world. Summon a gacha collection of bio-engineered defense towers, forge a custom loadout, and conquer three modes, story-driven Chronicle, roguelite Contracts, and 1v1 PvP Ascension. Tower defense meets deck-building meta-progression.

At a glance

• Platform: Windows, macOS, Linux.
• Genres: Indie, Strategy, Free To Play.
• Release date: Jul 17, 2026.
• Steam user reviews: Mostly Positive (71% positive).
• Delivered as a Steam library entitlement — activation is handled by Steam.

Minimum

Recommended

System requirements as published by the developer on Steam.

Activate on Steam

• Open the offer above — it takes you to this game's official Steam store page.
• Buy it there, or if you bought a key elsewhere, open Steam and choose Games → Activate a Product on Steam.
• Enter the product code exactly as it was issued to you.
• The game appears in your Steam library — download and play.

CDKeyCheap does not sell keys. We track and display prices; every purchase happens on the store you click through to.