My proudest achievement so far is a dumb-as-rocks little Clojure program that runs on a schedule in a free Heroku dyno. It sends alerts to a Slack channel when there's updates to a Trello board we use at work. All it does is ping Trello's API, check for changes in the new state against a Postgres Heroku add-on that stores the last seen state, and then send formatted messages based on the diff to a Slack channel for me and the few coworkers of mine who pay attention to it. It starts up hourly in a Heroku free dyno, runs for six or seven seconds (JVM lol) and then goes back to sleep. But I'm super proud of it because it's actually useful and I made it myself instead of relying on Zapier or IFTTT or something like that. It sparks joy for me every time I see that it ran correctly.
Now I'll have to find somewhere else to host the little thing, I reckon.