Loria (alpha)
siegment

Survival in hardcore acid-alien sci-fi themed world

Base Modpack
karlexceed

This combines several other mods that I consider a basic minimum starting point for worlds.

Caverealms Lite
Shara

A mod for Minetest to add underground realms.

Ethereal NG
TenPlus1

Ethereal mod uses the v7 mapgen to add many new biomes to the world.