TLDR: I built a free tool that reminds you to keep a healthy rhythm while breathing. It's called Breather and you can keep it open while coding.
Since this is a free tool that I specifically made for working at my desk as a developer, I hope this doesn't fall under self promotion. I truly just want to get this onto as many screens as possible, since I've found it very useful.
But of course I would be interested if you find it useful as well. I am open for any ideas and possible improvements!