In short, AutoBar adds one or more bars to your screen, each full of buttons for various categories. For instance, the default "main" bar has slots for:
- Hearthstone (and related abilities, like Death Gate or Scroll of Recall)
- Health potions
- Mana potions
- Buff foods
- Mage foods
- Elixirs (battle and guardian)
- Quest items
And probably some more things that I'm not remembering right now. AB shows the most recent item you've clicked for each category (in some cases) or the best item (in others), and other options in the category appear on mouse-over.
That's just the beginning, though. The bars are incredibly customizable, allowing you to move items between categories, create new buttons, set a preferred order, and so forth. You can even set up whole new bars if you want. You can bind keys to all the buttons (in the screenshot at top I have shift-B bound to bandage). AutoBar is also what actually provides the functionality I mistakenly attributed to Dominos to bind keys directly to spells in your spellbook, through a library it embeds.
There are also class bars set up; for instance, for my priest (at right), there are buttons for buffs, the class pet, shield, and a button labeled "ER" which I assume is meant to be an "oh no" button; it maps to PW:Shield on my priest and Vanish on my rogue. I don't tend to use the class bars because I have my skills bound how I like them already, but I'm sure they're useful for some people. And if not, it's easy enough to turn off.
AutoBar, like Dominos, supports cooldown counts via OmniCC and button skinning via ButtonFacade. It also has a neat feature for fading out when you're not hovering over it, which is useful because it tends to be full of buttons I don't need all the time. I have it currently set to fade out immediately, and become visible when I hold down control (or mouse over) so I can easily check cooldowns on trinkets and such.
It's also constantly updated. When Wrath first came out it didn't have support for a lot of trinkets and quest items, so I had to turn to other solutions (like a little Dominos bar with macros for /use 13 and /use 14), but at this point everything I've come across appears to be in there. There is another good solution for quest items, too: very soon on Addon Spotlight, we'll take a look at QBar.