This is my game, it's a tiny dungeon crawler played in the Windows file explorer. Your player character is a folder that you drag and drop into other folders to move, items are equipped by dropping them into your equipment folder, some items are used by deleting them, and monsters can be looted for their files.
I got the idea to do something in the file explorer after I saw this version of Flappy Bird in the Mac finder: https://github.com/nolenroyalty/flappy-dird
It was fairly straight forward to make, using just a file watcher, shortcuts, and (optionally) Window's explorer API to detect whether the player folder is open in an explorer window (to delay renaming the folder until it's not used). It only uses files and folders it creates itself, and doesn't look outside of its executable's folder.
The project lent itself very well to TDD, especially since there are a lot of interactions that are quite tedious to manually test again and again.
It's also available on Itch (no account required): https://juhrjuhr.itch.io/directory-dungeon