Calm - Calm.com can help you reduce stress and increase calm.
Breathly - Open-source breath training and relaxation app
SoundAura - A background audio player for studying / working.
Breathwrk - Science backed breathing exercises
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.
Calmaria - Breathing exercise for you to relax during this rough time