Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.
Headspace - Meditation made simple. Brilliant things happen in calm minds.
MyNoise - Custom shaped online noise machines. Many Many generic sounds
Medito - 100% Free Meditation App that will improve your Mental wellbeing with the help of Guided Meditations, Breathing Exercises, Mindfulness Practices, Relaxing Sounds, and more.
noice - Emoji Your Friends Can Hear (😃 + 🔊)
Calm - Calm.com can help you reduce stress and increase calm.