Breathly - Open-source breath training and relaxation app
Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.
Calmaria - Breathing exercise for you to relax during this rough time
MyNoise - Custom shaped online noise machines. Many Many generic sounds
Breathwrk - Science backed breathing exercises
noice - Emoji Your Friends Can Hear (😃 + 🔊)