iOS: You might need a floor plan of a room but you don't always have one handy. If you can't ask for one and don't want to go through all the trouble of drawing it yourself, an incredibly clever app called RoomScan can draw one for you in about a minute.
How? You just tap the phone against a wall, wait for a beep, and then tap it against another wall. As you move around the room you'll see your phone draw the floor plan. When you're all done, it will make some corrections to what you've accomplished by tapping and give you a finished image. It's really smart, easy to use, and available free of charge on the iTunes App Store for iPhone and iPad.