FOSS gamedev and creative worlds

Trying to find basic game with mapgen like old superflat in minecraft: at 0 layer of bedrock/scrith/whatever indestructible above that five layers of stone, above that three layers of dirt. As easy to mod as possible (no advanced stuff, i know almost nothing about lua), with lots of comments in code. Does a game like that exist or could someone make it?

I don't believe such a subgame exists. I might give it a go, but I absolutely suck at mapgen. I think that all you would have to do is register the bedrock node, and adjust the existing flat mapgen.

EDIT: minetest-tweaks and minetest_bedrock mods.