Music
I DJ, and I am a software engineer, so the hobby inevitably grew a system around it. Three pages came out of that - a map of the music, a way to look a track up against it, and a method for keeping the library in order.
Both are living documents rather than finished ones. They describe how I actually work right now, and I fully expect them to change as I play more.
Genres
Every style I actually play, on one shared tempo axis and as a family tree. Each one carries its BPM range, where it tends to land in a set, and the tracks, artists and labels that define it. I use this when I am digging.
Track Finder
The map read backwards. Give it a track and it asks four public music databases at once, then maps whatever they call it onto the genres above. Two sources agreeing is the answer; anything less says so. It runs entirely in your browser.
Music Management
How I keep the library organized: describing every track by what it does in a set rather than only what it is, keeping that description inside the audio files, and letting the playlists build themselves out of it.