Calm - Calm.com can help you reduce stress and increase calm.
Headspace - Meditation made simple. Brilliant things happen in calm minds.
SoundAura - A background audio player for studying / working.
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.
Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.
Smiling Mind - Promotes mindfulness and meditation for young people