Made in a few days for the Glorious Trainwrecks GDC Pirate Kart. It’s a mashup of Wolfenstein 3D and Minecraft, sort of a Wolf3D construction kit. Unfortunately it needs kind of a beefy PC. If the default level runs badly, you might have to stick to building your own little stage in the empty sandbox level.
Remember: Enter toggles creative mode, and you can open the crafting menu with Tab.
Edit: updated to v1.02, with some major performance improvements and bugfixes.