The EM drive (http://www.nasaspaceflight.com/2015/04/evaluating-nasas-futuristic-em-drive/), either the most exiting physics of a generation, or a measurement error.
Either way, the one thing most people agree on is the need for more testing. At the moment the design here presented is only useful for making interesting 3D printed models, it still needs work to turn it into a useful design that could be built for testing.
On that note: If you build your own EM drive from these files you do so ENTIRELY at your own risk. If you fry your nervous system with a converted Microwave oven it's your fault, and nothing to do with me.
The design is full-sized, so it'll need to be scaled down to fit on most printbeds. The full size design would require 60 M5 bolts to assemble, so scaling the files by a factor of 3/5 would allow the use of M3 bolts instead.
The full design uses 2mm think copper sheeting for the main body and 5mm copper for the end plates.