Test for building a Classic macOS app on MacOS X using ksherlock's mpw tool.
You need a built version of the mpw tool
built according to the instructions in their Wiki.
To run it, you need any MacOS classic Mac or emulator (i.e. MacOS 9 or earlier).
The C (.c, .h) and Rez (.r) source files use MacRoman encoding and MacOS line endings (ASCII 13) which GitHub doesn't display correctly (at least not yet; hopefully one day they will!). View them as "Raw" to have your browser show them correctly.