Hertz. is an application that coaches you to stimulate your vagus nerve, reducing anxiety, putting you at ease. It also provides biofeedback to increase your conscious control over your anxiety.
It consists of a focused breathing exercise. A red dot sweeps a dial of ticks. As the dot passes over blue ticks, you breath in, as it passes red ticks you breath out. Your heart rate variability changes the speed of the dot, this feedback will over time allow you to have greater conscious control over your state of anxiety.
Hertz. connects uses the HealthKit functionality of iOS to obtain the physiological data needed for biofeedback, if you decline to share data with the app it still functions but with emulated feedback.