The Paper Airplane Machine Gun, or Papierflieger-Maschinenpistole (yes, it was made in Germany), is made mostly from 3D printed parts. It takes sheets of paper, internally folds them into paper airplanes, and then launches them. It reminds me in the loosest sense of that gun in the upcoming CoD: Advanced Warfare that 3D prints its own bullets from a canister of “liquid matter”*. The future is clearly now.
*This link leads to the official campaign trailer for Advanced Warfare. The 3D printer rifle is used by the player for most of the gameplay – notice how the total ammo count slowly increases.