Spotify reminds me of Muzak in some ways. On the surface that might seem like a slight, as the term Muzak has become almost synonymous with the banal backing soundtracks to elevator rides, but the Muzak actually has a much more interesting history than you'd think.
In Elevator Music: A Surreal History of Muzak, Easy-Listening, and Other Moodsong Joseph Lanza dives into this history.
To bring the parallels to Spotify full-circle, I found their algorithmic approach to making mixes — back before we called them that — interesting. Did you want music to feel productive to? Happy? Romantic? Uplifting? Today you can peruse countless mixes created in automated way or by people all over the world, but Muzak was way ahead of the game.