WowAce

Raid level alternative player power warning (Atramedes, Cho'gall, Lord Rhyolith)

Fires events whenever a raid member "fails".

Aspect checker addon for Hunters.

A simple data broker display for current Artifact Power

Provides the ability to suppress specific spellcasts like "Deaden" from your casting bars.

Used to visualize and change values of variables/variable-trees in game

Omnibus

For Developers (of Addons which uses LibWho-2.0): show queues and queries in realtime

EnchantList

Battleground Timers in a HUD around the Blizzard BG status

Tooltip of socials button will now show which friends are online

Sneakily inspect how much gold your mouseover target has made so far.

GemCensus inspects people and records which gems they have socketed. Then displays which gems are the most popular.

Monitors the combatlog identifying players from the oposite faction near you.

LibRock-1.0

Displays info about who rolled Need/Greed/Pass on items that are currently rolled for

Heal and decurse by clicking on customizable raid/party unit frames

FuBar_FuXPFu

Note + rep tracking for players, with guild data sharing.

Considers an item against all the items you have to determine whether or not it is an upgrade