I saw a demo of a stereo lithography machine at our local community college. It's basically a 3-D inkjet that uses molten plastic instead of ink. You load a 3-D CAD file (an STL file) into the machine's computer and it "prints" the part in .010 thick layers. After the plastic hardens, you have a perfectly formed 3-D copy of the part. The detail and accuracy are incredible.
They use stereo lithography a lot in the machining/manufacturing world to develop prototypes in a day that would take months of lead time and many thousands of dollars the old way. The machines pay for themselves in no time.