Noizio - Feeling that the noise of the big city is too much for you to bear?
SoundSource - The sound control that should be built into MacOS
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.
Boom 3D - Audio enhancer with 3D surround sound
zenmix.io - Ambient background sound generator
A Soft Murmur - Ambient sounds to wash away distraction.