from sharable.net:
Today we’re on the verge of a factory in every home thanks to the RepRap, an open hardware 3D printer that is designed to replicate itself. You can make a RepRap for yourself, then use it to make one for your neighbor.
The design files and software needed to build and operate the RepRap are free. You can make one for about $500 in parts. And with each new version of the machine, an increasing percentage of the parts can be produced by the RepRap itself.