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.
Sounds of Earth - Listen to relaxing ambient sounds of nature
Noizer - Ambient sounds like Noisli, but free
Serene - The macOS app to get your focus back
Ambie - Beautiful white noise app to help focus, sleep, or meditate.
Shhh Noise - A free sound generator designed to increase focus and relaxation.