Composer Max Richter released Sleep in 2015, but it only recently became available on streaming platforms: Spotify, Amazon, Apple Music, Tidal. The album is 8 hours and 24 minutes long and was designed by Richter as a sleep aid/accompaniment. The composer worked with neuroscientist David Eagleman to align the music with the brain & body's natural sleep rhythms.
A snack-sized version of Sleep is also available: From Sleep, which clocks in at a mere hour long.