Professor Nial McCabe teaches Engineering Technology at the County College of Morris in Randolph, NJ. He has a web site with a large collection of engine plans that can be powered by compressed air or steam, plus a few other projects like the pin vise in the picture
The engines are not fancy and I don’t think they are intended to be. They are easy-to-build proven designs for teaching students basic machining skills. The McCabe Runner, his most popular design, looks a little crude, but the design of the valve appears to be easier to build and more tolerant of mistakes than some engines I’ve seen, such as oscillating engines that use small valve holes which need to be precisely located for them to run well.