When I was working at Acquia on the demo team, it became apparent that Drupal's native file handling was not exciting enough to impress clients coming from other content management systems. In response to this need, I decided to use existing Drupal 8 modules - Entity Embed, Entity Browser, and DropzoneJS - to create an experience that was good enough to show off.
The resulting project, File Browser, was essentially a demo of modules that the Drupal community had already built. What made it unique was that so much time was spent on the design and user experience that it looked brand new, even if the backend code was already widely used.
File Browser saw a massive adoption, the most of any Drupal project I've published so far, which is surprising because I've never spent too much time maintaining it. It's a great example of something small becoming popular unintentionally, where my more complex projects often languish and remain fairly obscure.
Project page: https://www.drupal.org/project/file_browser