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.
Ruya - A calming space
Noizio - Feeling that the noise of the big city is too much for you to bear?
zenmix.io - Ambient background sound generator
Spaces.FM Beta - Binaural sounds to improve focus and boost your productivity
Hear - Hear is a sound enhancement application for the Mac.