WowAce

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

A library to provide information about zones and instances.

an embeddable library providing an abstraction layer for tracking and querying Blizzard's Nameplate frames with ease and effi...

Test whether the player can really dispell a buff or debuff, given its talents.

Dropdown library for Ace3 options, extensible to other options formats. Works ok.

Provides data about all artifacts in the player's possession.

A library to help with localization of Zones.

Parses ToC and adds About panel to Interface options

StatLogicLib

A library to help with localization of classes.

Tooltip scanning library.

A library to track nameplates.

Manages the SavedVariables of your addon with a layered hierarchy of settings.

Library handling communcation for Magic* addons

A library to get currencies' related information

Configuration library

A library to help with localization of in-game item sets.

Library providing mouse-click support for LibQTip-1.0.

Talismonger-3.0

Helper functions used by my addons, feel free to use them in your addon too