My first BIG project: I lost the source code, but my first big project with school was a full Minecraft server for interactive learning for first years.
This included A LOT of Java code and new concepts like pathfinding. Now this was a 20-man team project, so I also learned to use GitHub, user stories, SCRUM, among other things.
We even had a test period where first and second year students came to test and play. Unfortunately we couldn’t finish it completely in the given timeframe and had to move on.