Caverealms Lite
Shara

A mod for Minetest to add underground realms.

Cloud Items
Panquesito7

Powerful cloud tools.

Multiple Biome Generator
chaosomnium

230 Pseudorandomly Generated Biomes, Trees, Fruits, Ores, Tools, and Liquids

Melterns
IcyDiamond

Tinkers Construct in Minetest!

Base Modpack
karlexceed

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

Alien Tools
chaosomnium

Alien Tools Mod for Minetest - adds Alien Tool, Shield, biome, etc

Obdy
Sires

Adds some pretty OP tools :)