Nice multifunctional designs—some production, some concepts—from the Belgian design studio of ID'er Alain Monnens, Idam Bvba:
The FlipTable (above) is simple, stackable, and flippable, tipping from desk height to side-table height.
The ServiceBin (manufactured by Wild Spirit) is a stool, or a wastebasket, or a storage bin, or a planter, and the top pops off to become a service tray.
The Bench 360 also is meant to be tipped, going from a curved seat for many to a rocking chaise longue for one.
The projects aren't directly linkable due to Flash (grrr) but you can see more of Monnens' projects here.