This is a Processing sketch, made in IntelliJ IDEA, that fills a 5x7 matrix with pixels that act like boulders: if they can fall on a side, they will. Once the matrix is full, it starts from scratch.
This is by no means a complete product. It worked on my Mac OS laptop, it may not work on yours.
I made this project based on an old attempt of mine to run Conway's Game of Life in RxJava and Kotlin on Processing. I abandoned that, and from its ashes I made this. Look at the commit history if you're interested to that attempt.