A comparison of these two addons.
A bag AddOn, with ludicrously-complex functionality.
ArkInventory is slow as fuck to log in with or open my bags/bank with. This is probably due to my heavy customization.
A framework for manipulation of the world map.
See also Cartographer vs Mapnotes
A floating "crazy-taxi" style arrow that points you to your destination.
An auction addon.
Overwhelming, ugly and unusable.
Allows you to select your chat text for copying.
Shift-click a chat frame to enter 'edit mode'.
Simple and effective.
Highlights links in chat, which can be clicked to put it in the chat frame edit box for easy copying.
The Ace libraries for World of Warcraft.
It has since become a whole community for World of Warcraft addon developers.
A bar/panel addon for displaying various bits of information.
I tried it and didn't see any real use for it.
Cosmos was a large bundle of AddOns which I really loved.