Created the first version of an app that took large long PDFs of train driver/conductor schedules in my country and presented them in an nice way in an app. The

Created the first version of an app that took large long PDFs of train driver/conductor schedules in my country and presented them in an nice way in an app. The previous sources were all hard to navigate and had ads. I spent a weekend parsing PDFs into SQLite, and shipped the app with a preloaded database. Then kept updating and tweaking and added some fun intersections of the data ("who else is operating this train"). 8 years later my source of data stopped providing data because of data protection concerns and the company introduced their own app/functionality for the same. Never earned me a dime directly but did get me my next job - it was a great sample for the interview