Autoloot was introduced in patch 1.9.0. If you <Shift>+click on a mob, chest, or other container that has items, you will automatically loot all non-bind-on-acquire items. You can also use the same method to automatically skin an animal, mine a vein, and harvest some herbs. This is now settable as an interface option as of patch 2.0.1, so that you might default to autoloot on a right click, without having to shift-right click to loot manually.
AutoLoot used to be an addon for Cosmos. It was removed once Blizzard introduced the <Shift>+click method of autolooting.
Patch changes[]
Patch 2.0.1 (2006-12-05): Added a setting option. 
Patch 1.9.0 (2006-01-03): Added.