Cool little aside in Marcin Wichary’s How to shoot a screen using a board of keys:

Acorn 8, a graphic app, has a delightful screenshotting feature parked under ⌘⇧7 that does something incredible: it takes a screenshot, but does so in a way where windows are separate layers, grouped by app. It’s amazing; you can re-compose stuff afterwards, reveal covered stuff, remove windows, even change the wallpaper. A mouse cursor arrives too in its own tiny layer, like a cherry on top.