A Space Age planet made of five terraces stacked like stairs, with cliffs you can't blow up. Sending things down a cliff is free, sending them up costs power.
Mods introducing new content into the game.
The art for Gradus, the Stairway World. It gets installed along with Gradus and does nothing by itself.
Lua libraries for use by other mods and submods that are parts of a larger mod.