Last year I wrote a simple component for React which let you create Instagram or Snapchat like stories on the web. It was just an impromptu idea and I wrote the whole thing in a couple of days. I posted it on ProductHunt and people loved it! It even got to the list of GitHub trending repositories and that left me ecstatic.
Over the time I improved the internal logic, refactored code and merged people's pull requests that did the same.