I wanna help you but i'm a bit lazy to search for it. It's a diablo 2 UI i think. Just go to wowinterface web site and use Diablo 2 as keywords to search for the addon.
I hadn't clicked on it and enlarged it before. But after seeing this thread I went and checked it out. It looks amazing idd. Very slick and clean. And thnx Imsdal for the refference.