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?
GitAmp - GitAmp is an open source project that plays a sound each time an event takes place on GitHub.
zenmix.io - Ambient background sound generator
Sounds of Earth - Listen to relaxing ambient sounds of nature
Hear - Hear is a sound enhancement application for the Mac.