WowAce

Library providing mappings between trade skill recipes, spells and created items

Automated smart raid marking to speed up trash clearing in instance runs

Books in Azsuna? Sure, why not?

A replacement tradeskill window

Deus Vox Encounters

Wowhead Data dump for GatherMate

Quest History tracker and shows lists of quests in each category

Queing of /who and SendWho() queries and a much better interface (see docs), with gurantee to be executed & callback.

Track time played, rested XP and money for all characters

Blocks Chinese Chat

Unit Frames of awesomeness. Woof. It'll bite your face off.

A library to provide mobIDs for bosses.

Show item durability and quality in the character frame.

Additional information about player spells.

Displays information about the current zone on the World Map, for WoW TBC Classic

Simple and super light-weight tracking of profession links for all your alts.

Alternate Power- and Combopoint/SoulShard/HolyPower-bar

Try on different gear and see their total stats and their differences. In short, an ingame CT-Profiles-like addon.

Shows you a much bigger icon selection frame

Database of Vendor locations for HandyNotes