It uses layered worlds, similar to Realms. I've tried to make the biome/decoration code as close to the minetest game as possible. It can even spawn coral and other water decorations. However, there are still a few missing features.
The realms.conf file, which you must copy from realms.conf.example, contains all the data about where each type of terrain occurs. It can be edited as plain text, and matches the format of Realms, except that you may use a number sign at the start of a line to denote a comment.
At the moment, the worlds included are:
dflats: A simple terrain with hills, seas, and a lot of flat space to build on. It includes a mysterious network of tunnels underground.
islands: Copied almost verbatim from Termos' Islands mod, but using my biome generation. This is my current zero-world. (I love the terrain.)
Ores are generated differently from the game, in simple, sparse cubes throughout the terrain. Usually, digging deeper will get you better ore (but not more).
The source is available on github.
Code: LGPL2, GPL3, textures: strictly CC0
Mod dependencies: default, geomorph
Optional: bucket, match_three, flowers