: A DRM-free version is often available at a discount on the GOG website .
A heavy metal door hissed open, revealing a vast, dark chamber filled with floating platforms and conveyor belts. A robotic voice, cold and devoid of empathy, echoed through the room: "Subject 42, begin assembly. The Overlords require their tribute. Failure is... inefficient."
is a sandbox puzzle game where you build complex factories for alien overlords. While it is not currently free, you can find it and follow its story-driven campaign on several platforms: