Remember Napster or Grokster? Both services allowed users to share computer files – usually digital music – that infringed the copyrights for those songs. Now imagine that, instead of music, you could download a physical object. Sounds like something from a sci-fi movie – push a button and there’s the item! But that scenario is already becoming a reality. With a 3D printer, someone can download a computer file, called a computer-aided design (CAD) file, that instructs the printer to make a physical, three-dimensional object.