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.
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.
Noizio - Feeling that the noise of the big city is too much for you to bear?
Sleep Bug - Sleep Bug is the name of an ambient sound mixer that generates a wide range of scenes and music using the random sound effects.
zenmix.io - Ambient background sound generator
Noises Online - Premium masking sounds