WowAce

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

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

Toss those bugs inna sack.

Database of item upgrade IDs

Library that handles chat output.

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

Postal: Enhanced Mailbox support

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

Replacement for the default UI's StaticPopup dialogs.

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

Parses ToC and adds About panel to Interface options

Modular casting bar.

Displays additional information for Mythic Keystone dungeons

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

Restores access to removed interface options in Legion

Chat addon, filtering messages and UI changes

Show item levels in the character frame

Tracks rare drops, including companions and mounts

Makes the default frames moveable via simple drag and drop

Replacement for ActionButton_Show/HideOverlayGlow APIs