WowAce

Library providing multi-column tooltips.

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

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

Chat addon, filtering messages and UI changes

A library for transmitting and receiving latency information of players.

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

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

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

Modular casting bar.

Give whispers an instant messenger feel.

Displays additional information for Mythic Keystone dungeons

Replacement for the default UI's StaticPopup dialogs.

Library that handles chat output.

The original source for where things are in Pandaria

Restores access to removed interface options in Legion

Show item levels in the character frame

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

Parses ToC and adds About panel to Interface options

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