Nothing more or less than a genuine 3-D pen. That's pretty cool.
Caution: (1) Do not use 3Doodler while drinking tequila. Attempting to operate 3Doodler while drinking tequila may result in four-dimensional perception, objects, and/or travel. Advanced techniques such as this should be left to skilled professionals. (2) Do not attempt to draw tesseracts in or near fault zones with 3Doodler. Narrow but humorous escapes may result.