Libraries:

Discord.js

A JavaScript library for Discord.

Discordgo

Go bindings for Discord.

discordrb

A Ruby library for Discord.

Sword

A Discord Library for Swift

RestCord

A PHP REST library for Discord.

DiscordPHP

A PHP REST and WebSocket library for Discord.

Javacord

A multithreaded but simple to use discord java api.

discord.py

A Python library for Discord.

serenity

An Rust library for the Discord API.

DSharpPlus

An unofficial .NET wrapper for the Discord API, based off DiscordSharp, but rewritten to fit the API standards.

Discord.Net

A C# library for Discord.

Discord4J

A Java binding for the Discord API.

discordie

A Node.js module providing a set of interfaces to interact with Discord API.

discord-rs

A Rust library for the Discord API.

Discordia

Discord API library written in Lua for the Luvit environment

eris

A NodeJS library for Discord.

discord-hs

A Haskell library for Discord.

discordcr

A minimalist Crystal library for Discord, focused on performance and control rather than ease-of-use.

JDA

A Java wrapper for the Discord REST and Websocket API.