For me, building a visual "thing counter" was an excellent project:

[1] https://taylor.town/livecount

(Skip to 0:59 if you want to see the actual demo without the configuration.)

In order to run at a high framerate, I implemented 100% of the code from scratch in Swift. There's no OpenCV or any third-party dependencies in there.

I'm not working on it anymore, so if y'all wanna use it is as a starting point for improvements, send me an email at hello@taylor.town