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

Noisli - Noisli is a fantastic background noise and color generator for working and relaxing. Online soothing ambient sounds like White noise, Rain and Coffee Shop.