Transparent Desktops

Have you ever been watching Only Fools And Horses show? Can you remember Del Boy's famous sentence "Bloody Hell"? Well I refreshed my memory on that one when I saw these things; it was the first thing that came out of my mouth "Bloody hell, how did they do this!?" Then all sorts of things started to flow around my head - "Could it be true? Can they really somehow make those screens transparent?