Ballast is a paced-breathing app for iPhone and Apple Watch. You set the rhythm - box breathing, 4-7-8, or a pattern of your own - and it paces you through it and keeps your session history on your device.
Questions, bug reports and feature requests all go to one place: evanator@me.com. It is read by a person, and it is the same address named in the privacy policy.
What the app stores, what it never sends, and how to turn any of it off is written out in full in the privacy policy.