Over at Thingiverse, user mattmoses has developed an impressive homebrew electric motor design. From the project page:

This is an electric motor made from a printed circuit board, some 3D printed components, 44 magnets, 44 steel washers, and a handful of electronic components for drive circuitry.

It is similar in design to thingiverse.com/thing:802 but it is much easier to make and the performance is much better. Maximum mechanical power output is about 600 mW. Top no-load speed is about 2000 rpm. This is probably enough power to do something useful.

Also provided is an open source script that runs on Matlab or GNU Octave to generate custom motor coil patterns. The script will export CAM files in KiCad or EAGLE format, so you can fabricate coil patterns of your own liking.

While this motor used a commercially produced PCB for the coilplate, the idea is that users can produce functional motors using nothing more than their own 3D printers.

Videos of the motor in action can be found on YouTube and are embedded below:

(Thanks Marc!)