I built my first database-backed website in 2000, a site called The Lab Archive. It was a place for chemistry instructors on a popular listserv to upload their handouts and lab protocols. (This was before Google Drive. This was almost before Google. It wasn't all that easy to put files online and have people find them.)
Visually, it hasn't aged well. A lot has changed in terms of our standards for websites in the last 20-something years!
Features I was proud of: User authentication, file uploads, ratings system, comments.