Headspace - Meditation made simple. Brilliant things happen in calm minds.
Moszen - Moszen is a free web service that provides ambient sounds from natural environments to help you relax and avoid stress in your daily life.
Calm - Calm.com can help you reduce stress and increase calm.
Noises Online - Premium masking sounds
Mezmind - Calming Interactive Environments
SoliCall Pro - Removes noise & echo from any VoIP call. Can also be used for call recording.