WowAce

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

A library allowing for easy creation of graphs

A library for transmitting and receiving latency information of players.

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

Postal: Enhanced Mailbox support

Grabs bugs for the bug sack.

Tracks rare drops, including companions and mounts

Database of item upgrade IDs

Chat addon, filtering messages and UI changes

Library that handles chat output.

The original source for where things are in Pandaria

Makes the default frames moveable via simple drag and drop

Replacement for the default UI's StaticPopup dialogs.

Modular casting bar.

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

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

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

Parses ToC and adds About panel to Interface options

Arena unit frames

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