The Stirling cycle engine post reminded me of these solar furnaces. Under the right conditions they can produce a great deal of heat without much in the way of complicated machinery. A few generate enough heat to melt steel, and smaller versions can be used for cooking or heating water.
Stereotactic radiosurgery (AKA Gamma Knife) takes advantage of the same property of light to focus intensely. In this case it is exploited to be able to kill brain tumors without having to cut through healthy tissue, since the intensity is so low for each individual beam, but very high where all the (dozens of) beams intersect. Always thought that was a cool use of science. Though in this case, there’s really no such thing as focusing x-rays/gamma radiation. It’s done through collimating of radioactive sources.