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S.A.C.K. - Survive and Choose Knowledge
You are a backpack fighting alien swarms on an expanding moon base. Build your loadout from unique weapons and towers, deploy turrets within your build limit, choose boss evolutions, and get permanently stronger. Bullet Heaven meets Tower Defense!

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Features
Single-player
Family Sharing
Profile Features Limited 
Languages:
Interface Full Audio Subtitles
English ✔

Coming Soon To Early Access

The developers of this game intend to release as a work in progress, developing with the feedback of players.

Note: Games in Early Access are not complete and may or may not change further. If you are not excited to play this game in its current state, then you should wait to see if the game progresses further in development. Learn more

What the developers have to say:

Why Early Access?

“S.A.C.K. is being developed by a solo indie developer, and I'm honest about the fact that development speed and continuity depend on my personal situation — I'm currently between jobs and can't guarantee how much time I'll be able to dedicate to the project going forward. Early Access lets me get the game into players' hands now, gather real feedback on balance and content direction, and keep development sustainable with your support, rather than disappearing into years of silent solo development.”

Approximately how long will this game be in Early Access?

“Realistically, I expect S.A.C.K. to stay in Early Access for around 12 to 24 months. That's the time I estimate I'll need to add enough content and properly polish and balance the game — though as a solo developer, this timeline may shift depending on circumstances.”

How is the full version planned to differ from the Early Access version?

“During Early Access, we plan to expand the roster of bosses and enemies, add more weapons and card rarities, and build out the meta-progression shop with additional permanent upgrades. We're also refining the game's visual style and continuing to improve UI and menu systems based on player feedback. Core gameplay systems are already in place, but content volume and balance will grow significantly by full release.”

What is the current state of the Early Access version?

“The core gameplay loop is fully playable: survive waves of enemies, collect rarity-based upgrade cards, unlock weapons, and face off against boss encounters. A persistent power-up shop between runs is already implemented, along with a pause menu and stats overview. The game currently includes a limited set of bosses, weapons, and enemies, with more planned throughout Early Access.”

Will the game be priced differently during and after Early Access?

“We plan to start at a lower price during Early Access and gradually increase it as we add more content and features. The price at full release will be higher than the Early Access starting price, so joining early is also a way to support development at a lower cost.”

How are you planning on involving the Community in your development process?

“I stream development regularly on Twitch and post devlogs on YouTube — mostly in German, though I try to keep things accessible with visuals and captions where possible. Suggestions and ideas can be submitted via Discord, and I also keep an eye on Steam's built-in community tools. I read everything, and where it makes sense I implement good ideas directly or find a compromise that fits the game's direction.”
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About This Game

You are the backpack. The galaxy is your problem.

S.A.C.K. drops you as a living backpack onto an abstract moon surface, surrounded by relentless alien monsters. Your only goal: survive, adapt, deploy your defenses, and come back stronger.

Bullet Heaven Meets Tower Defense

Battle through massive swarms with a fully customizable arsenal of up to 6 unique weapons and towers in your inventory.

  • Your Tower Limit: You have a max limit for active towers on the map. Upgrade this limit as you level up!

  • Total Deployment Freedom: Use your unlocked towers however you want within your limit. Have 3 different tower types in your inventory? You can place 4 Fire Towers and 2 Baseball Towers, spam 7 Standard Towers, or ignore towers entirely and rely purely on mobile firepower.

Your Base Grows with You

Every 5 levels, you choose a direction to expand the map. Expanding gives you more space to place towers and dodge enemies, but beware: every expansion introduces new obstacles and portals that send fresh alien waves your way.

5 Bosses + 1 High-Score Boss

  • Boss Evolutions: Defeat up to 5 unique bosses per run. Every victory rewards you with a choice of powerful evolutions for your weapons and towers, while introducing tougher enemy types to the map.

  • The Final High-Score Boss: Survived all 5 bosses? Prepare for the ultimate test. The final boss is an unbeatable menace designed solely to challenge your complete build and push your high score to the absolute limit!

Upgrade Cards & Permanent Progression

  • In-Run Upgrades & Rarity Tiers: Level up to draft randomized upgrade cards (featuring common to legendary rarity tiers) to raise your tower placement limit, boost stats, or empower your arsenal.

  • Meta-Progression: Collect gold dropped by aliens to buy permanent stat upgrades between runs—increase your damage, range, build limits, and survivability.

Key Features:

  • Custom Loadouts: Up to 6 unique weapons and towers in your inventory to mix and match.

  • Flexible Tower Deployment: Place your unlocked towers freely on the map up to your current tower limit.

  • Expandable Map Grid: Expand your map every 5 levels for more placement space—and new enemy portals.

  • Boss Evolutions: Defeat 5 bosses to claim run-changing weapon and tower evolutions.

  • Endless High-Score Boss: Challenge an unbeatable final boss to show off your ultimate build.

  • Card Drafting & Rarity System: Pick in-run upgrades with distinct rarity tiers.

  • Permanent Meta-Progression: Use earned gold between runs for permanent stat boosts.

  • Charming Visual Style: A stylized mix of pixel-art effects and clean vector graphics in a family-friendly alien setting.

AI Generated Content Disclosure

The developers describe how their game uses AI Generated Content like this:

This game uses generative AI to create part of its visual content. Specifically, AI tools were used as part of the graphics workflow to generate concept and source material for sprites and artwork, which were then manually reworked, adjusted, and integrated into the final game using Affinity Designer.

System Requirements

    Minimum:
    • OS: Windows 10
    • Processor: Intel Core i5-7400 / AMD Ryzen 3 1200
    • Memory: 8 GB RAM
    • Graphics: NVIDIA GTX 1050 Ti / AMD Radeon RX 560
    • Storage: 5 GB available space
    • Sound Card: DirectX-compatible
    Recommended:
    • OS: Windows 11
    • Processor: Intel Core i7-9700K / AMD Ryzen 5 3600
    • Graphics: NVIDIA RTX 2060 / AMD RX 5700 XT
    • Storage: 10 GB available space
    • Sound Card: DirectX-compatible
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