WowAce

Database of item upgrade IDs

Grabs bugs for the bug sack.

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

Chat addon, filtering messages and UI changes

Displays additional information for Mythic Keystone dungeons

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

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

Makes the default frames moveable via simple drag and drop

Tracks rare drops, including companions and mounts

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

Replacement for ActionButton_Show/HideOverlayGlow APIs

An intuitive keybindings library.

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

Restores access to removed interface options in Legion