There’s a bike valet service at a hospital in Portland. About 300 people use it every day to get to work. I made the web app and a few other tools using Google Apps Scripts that make it easy for the valet attendants and customers to check their bikes in and out, send automated emails and text messages.
It’s fun to have made something that so many people actually use and that I hope makes the world a little bit better. Plus I’m a completely self-taught programmer (my day job is content strategy) and it was rewarding to work on a bigger project than the little scripts/games/etc. I usually make for myself.