WowAce

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

Creates and manages secure Action Buttons

A library to help with localization of in-game subzone names.

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

Tracks rare drops, including companions and mounts

Modular casting bar.

Shared handling of alternate identity data between addons.

Provides one or many frames for dumping text into.

Arena unit frames

A library to help with localization of the output of UnitCreatureType.

Show item levels in the character frame

Replacement for the default UI's StaticPopup dialogs.

"Debug" code free since '93!

Simple Map Mod

Restores access to removed interface options in Legion

A library to help with localization of races.

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

A skinning engine for button-based add-ons.

A library to help with localization of bosses.

Adirelle's bag addon.