Let It Rain was my first serious coding project I actively worked on while in high school. It's a simple match-3 style game with a functioning level timer and colored tiles corresponding to the amount of times the player still needs to match bubbles on top of them. Let It Rain was programmed in Python 3, the first programming language I worked with, with the help of Pygame to do most of the sprite and rendering work.
By the time I stopped working on the program, I had learned how difficult working all in one file becomes, especially when debugging. Splitting classes, functions, etc. into multiple files helps a lot with organization (as well as with the coder's sanity!).