An open source(ish) fitness tracker would be great. I like the idea of being able to write apps for my Apple Watch to add custom features (I.e. automatic rest t

An open source(ish) fitness tracker would be great. I like the idea of being able to write apps for my Apple Watch to add custom features (I.e. automatic rest timers when weightlifting) but don't want a smartwatch or soemthing with that small of a battery. A WHOOP that I don't have to pay monthly for and can get some programmability out of would be great