Not directly for myself, but a friend who has a small event business.

I created a web based mobile ticket scanner.

They said the ticket companies would take huge subscription fees for their scanners and they didn't need all the features they offered.

So, I bought a 30€ Bluetooth scanner, wrote a small UI that allowed them to create events and check that each ticket is only scanned once.

Of all my software, this is probably the most regularly used one, lol.