WowAce

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

Library that handles chat output.

Toss those bugs inna sack.

Simple and Advanced combined - Bartender4 ActionBar AddOn

Replacement for the default UI's StaticPopup dialogs.

Postal: Enhanced Mailbox support

Parses ToC and adds About panel to Interface options

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

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

Displays additional information for Mythic Keystone dungeons

Chat addon, filtering messages and UI changes

Library to check whether an item is equipable / appropriate for a given class

Replacement for ActionButton_Show/HideOverlayGlow APIs

Makes the default frames moveable via simple drag and drop

Tracks rare drops, including companions and mounts

Restores access to removed interface options in Legion

An intuitive keybindings library.

Modular casting bar.

Creates and manages secure Action Buttons

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