FS51
Luke

Compatibility layer for formspecs

name monoid
fluxionary

flexible control of a player's nametag

CentralAuth
1F616EMO

Player account unification across Luanti servers

action queues
fluxionary

provides an API for queuing things for batch processing w/ various ways to specify the batch "size".

Seasons Clock
solsword

API for getting various "season" parameters based on server time and a few customiable settings. Doesn't change gameplay; just a library that other mods can use to do seasonal things.

hand_monoid
fluxionary

player monoid for controlling the look and abilities of the player's hand.

Persistent Effects
epCode

An API for creating persistent effects for any object. eg. damage a player or entity over time. (like poison)

CSMT Bots (Obsolete)
Logikí

Add bots to your game for training

Fbt Core
Forburnt

A set of utils for other fbt_* mods

Cid Music Player
ekl

Plays music

MFSM Multiple Finite State Machine
Sumi

Allows for multple states to be active, while maintaining typical state machine behavior. Good for gamestate and mobs.

TPH's Basic Filesystem
TPH

API for loading files into a basic readable format as well as loading and converting conf files

Table Goodies
benrob0329

A small package for extra (can't live without) functions for working with tables.

Antigrief
sorcerykid

An API for validating node and item placement via a simple callback mechanism.

Bedrock Markup Language
sorcerykid

Bedrock Markup Language is an extensible markup language and API for formspecs.

Compression Lib
The4spaceconstants

A library that provides functions to procedurally register compressed versions of nodes.

Kill Log
Wuzzy

Allows mods to display the recent player kills, deaths and other game events

Smart Vector Table
Noodlemire

API that adds a way to create tables indexed by 3D Vectors.

deploader
LuantistDork

Simple mod API that automates dependency-specific behaviour using a folder-heavy approach.

Node Damage
Noodlemire

Enables nodes to be partially damaged, and to be repaired afterwards.

craftsystem
fluxionary

craft registration API which automatically deals w/ replacements

Minetest Systemd (API)
Piezo_

Debugging utility and compatibility tools for server owners and/or modpack creators

Function Delayer
Hybrid Dog

Allows executing functions after a delay to reduce possible lag (EDD scheduler?)

Complete and Total Lua-Only Inventory Rewrite
Noodlemire

Creates a completely custom inventory system, which doesn't rely at all on any of the usual UserData objects.

Advanced Rangefinder
sorcerykid

Extends the API with search capabilities for entities

Lush
rstcxk

fully featured shell interpreter

Noriel Sylvire's Minerals Core Modpack
Noriel_Sylvire

An API for automatically registering recipes, nodes and ore generation.

timehud
bookgirl

Minimal HUD timer API

YAML Config File Library
snowyu

Load or Save YAML config file

GroupLib
rudzik8

General grouping API

Telegram
neko259

Integration with telegram messenger chat

Item Tracking
Impulse

Provides a API to mod developers to track which inventories items are in.

Minebase Core
ThatCommand

Adds APIs and new dynamic functionalities.

Isogen
BuckarooBanzai

Generate isometric images from ingame builds

Tips
1F616EMO

Send tips to newcomers

Face Objects
1F616EMO

Calculate the facing of objects

Wield Events
mt-mods

Events for wield item switching

Autobox
Just_Visiting

Auto Collision/Selection Loading Boxes

Node Object
jwmhjwmh

A library for associating objects with nodes

Priority Queue
Wiz

Associate items with priorities to order them.