Shelling corn is a chore done by hand in much of the rural developing world. Corn comes in different sizes - and the various DIY shellers are a major chore to make. Here you can either use the customizer app or the OpenSCAD to get the right size of sheller for your crop -- then print in plastic or metal.
This is an example of 3-D printable open source appropriate technology developed byMichigan Tech's Open Sustainability Technology Lab.
This academic paper explains how 3-D printing could be a powerful tool for pulling people out of poverty in the developing world.