About six months ago, the source code to Mod4Win (a module player for Windows) was made available by its authors: https://github.com/shamblernaut/Mod4Win

There's a lot of module player code already out there, but I remember, as a kid, being fascinated by Mod4Win's interface, which was very unlike any other Windows program I'd used before. (There's an imagemap version of the UI at http://kay-bruns.de/mod4win/mod4win/index.htm.) Almost 30 years later, I can peek into how it was built...