Backpack
The number in the top right corner shows the number of empty slots in this location. This is one of the possible ways to arrange items: Shows all items grouped by their auction house category.
Onebag Display
One of the possible ways to display items: This one is the "all-in-one" view.
Enhanced item tooltip
Adds extra information to item tooltips showing which of your characters own the currently displayed item.
Database search
A browsable search window showing all your items matching the given search string owned by any of your characters on the same shard and faction.
Empty slot indicator
Shows the number of empty inventory slots over the backpack icon in the bags window.