I've written previously about using Hazel on macOS to react to a new file appearing in a synced iCloud Drive folder and running commands. But I wanted a faster solution that I could trigger from almost anywhere - including an iOS Shortcut. A way to send a command directly from my phone (or maybe any other device?) to my Mac.
What I came up with is a tiny, macOS menu bar app I call Shelley - because as a friend told me, it's a Frankenstein of a hack.