Via the Verge, this is Quasar, a jailbreak mod for iOS that gives your iPad moveable, resizable, non-full-screen windows, just like a mouse-based operating system. It turns the iOS homescreen into a full-fledged desktop. Well, a medium-fledged desktop. A desktop.
Quasar is either a blasphemous affront to the iOS design philosophy or an crude glimpse at what a converged OS X/iOS operating could look like; in any case, it's $10 and requires that you jailbreak your iPad, and its only real guarantee is that it will be pretty buggy.
I like this as a piece of alternate history. It's what might have happened to iOS if Steve Jobs, Jony Ive and Scott Forstall were significantly lazier, or at least less incredibly stubborn.