WowAce

Scan for rare mobs so you can find them and their loot

Toss those bugs inna sack.

Restores access to removed interface options in Legion

Makes the default frames moveable via simple drag and drop

Tracks Raid/Instance/World Boss lockouts for all your characters, daily/weekly quests, currencies, trade cooldowns, and more!

Afflictions display and cleaning for solo, group and raid with advanced filtering and priority system.

Tracks rare drops, including companions and mounts

Simple AceGUI3 dropdown item classes for font/statusbar/sound/etc.

A library for transmitting and receiving latency information of players.

A library for transmitting and receiving durability information of players in your group.

A modular, lightweight and screen-estate saving grid of party/raid unit frames

Library that handles chat output.

Keeps track of group members and keeps an up-to-date cache of their specialization and talents.

Database of item upgrade IDs

Give whispers an instant messenger feel.

Officially the original source for where things are in the Broken Isles, in HandyNotes

The original HandyNotes source for where things are in Battle for Azeroth

The original source for where things are in Pandaria

Show item levels in the character frame

A skinning engine for button-based add-ons.