WowAce

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

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

Database of item upgrade IDs

Toss those bugs inna sack.

Library providing multi-column tooltips.

Library that handles chat output.

Give whispers an instant messenger feel.

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

A framework for chat enhancement modules.

Postal: Enhanced Mailbox support

A library to determine estimated range.

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

Collects Herbs, Mines, Gas Clouds, Archaeology, Treasure and Fishing locations and adds them to the worldmap and minimap

Collects Herbs, Mines, Gas Clouds, Archaeology, Treasure and Fishing locations and adds them to the worldmap and minimap

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

Modular casting bar.

Where are the hidden treasures in Legion?

Adirelle's bag addon.

A skinning engine for button-based add-ons.

Arena unit frames