I repurposed an old microwave with the intent to make a microwave gun. When I first had the idea I had an initial delusional vision of it being able to be effective at considerable range, but unfortunately the math just doesn’t hold up. Just the same I studied the design principals of a properly sized wave guide and how to position the magnetron to set up a standing wave and best direct the radiation and built a calculator to size for this particular build.
All in all, it can light a florescent tube you wave in front of it at about 6ft or so, which is kind of fun; all while making the requisite light saber sound effects of course!