AddOn development framework
A basic introduction to usage can be found here:
http://www.wowace.com/addons/ace3/pages/getting-started/
Documentation can be found here:
http://www.wowace.com/addons/ace3/pages/
For historic purposes, the "old" documentation is still around on the old wiki, some articles may not be converted yet, and only exist on the old wiki:
http://old.wowace.com/wiki/Ace3