WowAce

Shows Item Level and Stack Size in tooltips

CatFight

agUF style oUF layout

Allows movement and scaling of class-specific resource displays

Guild members

Skills plugin for any DataBroker display.

A set of datatexts for ElvUI that provide you with detailed info about your professions

Intended to be a complete guild management tool suite)

BetterMagnet

Cartographer_Import

Automatically sends guild recruitment ads to the GuildRecruitment channel.

Simple embeddable publish-subscribe implementation.

WindowLib

FuBar_XPerlFu

Repairs your items automatically upon visiting a vendor.

Adds an icon to item, spell, and achievement links

Allows communication to be shared across realm through Battle.net.

oUF_Castbar

Combat Alert

What actual item level is an item? Yes, it's horrible we need a library for this.