Moblib
LMD

Low-level high-performance entity library

Modding Library
LMD

Multipurpose Minetest Modding Library

Advanced Trains
orwell

Adds good-looking, realistic trains with realistic rails.

Mob Core
mt-mods

A Mob API meant to expand upon mobkit and bring easy to use features for creating new Mobs.

Library Mount
Panquesito7

API Framework for mounting objects.

Epic
BuckarooBanzai

Enhanced Programmer for Ingame Control

Formspec AST
Luke

A library to help other mods interpret formspecs.

Subcommands
1F616EMO

API to make commands with subcommands

Timed World Modifiers library
karamel

Environmental ABM that could be triggered on a very wide range of nodes but only a few at a time.

Autobox
Just_Visiting

Auto Collision/Selection Loading Boxes

Cellestial Game
LMD

Game of Life in three dimensions.

Natural slopes library
karamel

Library to simply add slopes to regular nodes and include them on map generation and when changing the landscape.

Position listeners library
karamel

Players' position observing library

Vision Lib
mt-mods

Common library for PolySaken's mods.

arena_lib
Zughy

Library to create any mini-game you have in mind