I was watching Systems with JT the other day and he demoed a hobby operating system called skiftOS. During the demo he ran one of the built-in apps called "neko" which looks like a clone of an old Windows "pet" program I remember from my childhood, also called "neko" (or "neko32").
It's a really simple program: when you start it up, a cute little kitten shows up on your screen and starts running around, trying to catch your mouse cursor. I figured it would be fun to clone the program for macOS and so I went ahead and spent most of yesterday doing it. Here's the code and if you're feeling nostalgic and want to run it yourself, you can grab a build from the releases tab.