It would be a huge undertaking, but a Fitness and Health tracker / aggregator that could replace Google Fit and the likes.

I really can't bear how Google, Apple, Samsung, and all these big companies are the primary holders of our most intimate information. I've put some measures in place to limit who gets what, but it would be a huge boon to be the sole maintainer of my own info.

The problem is that the various apps and devices which report data won't immediately support syncing with a FOSS upstart...

The app I use for grabbing my weight and BMI can only sync with a few other apps. The app I use for calorie and diet tracking can likewise only sync with a few apps. They happen to have Google fit in common, so I use that as an intermediary to transfer weight to the calorie/diet app. All my steps, exercise, and sleep stay in Zepp, separate from them all.

It sure would be nice to have one service/application to rule them all and a secure method of storing one's own personal information without having to give it to the tech companies. Sure, use one of the many cloud services but encrypt all the data so that they can't steal it. Yadda yadda.

One can dream.