Ask HN: your one-off HTML applet tailored to personal use?

I recently had to frequently log stuff with my phone while outside, so I wrote a ~30 line HTML form that is just an input box and three buttons (Timestamp/Newline/Clear) that lets me quickly log a message. Turns out that making it into an offline PWA is just a matter of adding a short manifest and a sw.js for cache requests, and two lines of localStorage for persistence, so now I have a trusty app on my phone that’s the digital equivalent of a carpenter’s self-crafted ugly-but-works shop tool. It felt good that hand-rolling a barebones HTML app is actually so easy, giving me a new appreciation for the webstack if you don’t overcomplicate it into a car made from Legos. What are some of your tailored-for-personal-use hacky toolets that leverages a minimal use of vanilla webstack?