Music and Lyrics
A few months after C was born I had the idea that at some point I'd want her to be able to play music by herself without my help (and without a screen), just like I was able to with physical tapes and records when I was little. Originally my plan was to do this with QR codes or NFC tags on physical objects, but I ended up dropping that path and just using a numeric keypad, like a jukebox.
Newer projects like Yoto, Yaydio, Roomie, and TagTuner are more polished, but this has done the job every single evening since 2015 with zero problems.
dmd
It ended up mainly as a way to play bedtime music; I typically add a new playlist every few months.
I also generate a lyrics sheet for the kids; I keep the lyrics updated in a Markdown file, and then pandoc → weasyprint plus some css generates a PDF.