We had 24 hours to work on an idea that would help the citizens of my home town, Brasov. Because then, google maps didn't have bus route helper, me and my team decided to implement this.
It basically tells you what buses to get from point A to B (even if you need to switch buses). Also it provides you a rough estimate with how much time the trip is going to take you.
The Project was realised in High school (10th grade), in a team of 4 during a 24 hours hackathon where we got the 1st place. I wrote the backend functionality.