It's a little ball that lives in your dock. You can drag it, and it'll bounce around the screen. You can flick it, bounce it, try to make it hit the corner, count how many times it hits the wall, and more. It's a ball. It's fun. It's a ball.
Saw this on Twitter (X) and it looked fun...but I grossly underestimated how addicting and cool it is. Really neat application of using the dock to create an immersive experience on a laptop.
I highly recommend folks to try this out if not for the joy of bouncing a ball, to add a new way of thinking on how to build Mac apps.