“BumpTop is a desktop environment supporting normal behavior of a real-world desk. It is aimed at stylus interaction, making it more suitable for tablet PCs and palmtops.  In BumpTop, documents are described by three-dimensional boxes lying on a virtual desk. The user can position the boxes on the desk using the stylus or mouse. Extensive use of physics effects like bumping and tossing is applied to documents when they interact, for a more realistic experience. Boxes can be stacked with well-defined gestures.” Source