The 3Doodler, a new 3D printing pen from the toy and robotics company WobbleWorks, lets users transform sketches into three-dimensional objects. The pen, currently in development thanks in part to a successful Kickstarter campaign, emits ABS plastic instead of ink. Once plugged in, the device lets you draw on a surface and peel away the plastic after it cools and solidifies. You can then build on a framework by drawing three-dimensional designs in the air. The company has demonstrated the pen by creating jewelry, fridge magnets, and a mini Eiffel Tower. If the 3Doodler delivers as advertised, back-of-napkin sketches may soon turn into impromptu prototypes.