Printrbot Extruder by Brook Drumm is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
I have chosen to license this and all my designs under a non-commercial license. This is currently the best choice for us to be sure the files get out there, but offer protection against people selling our 3D printers and damaging our reputation and brand.
If you are an individual, a school, a club, a hackerspace, makerspace, fablab….. we hope this helps the people in your community make thier own Printrbot! But keep in mind you can’t sell them. 🙂