In the 1960s, La Monte Young wrote a piece entitled The Well-Tuned Piano, a riff on J. S. Bach's The Well-Tempered Klavier. It features an equally-tuned piano, so each interval is mathematically correct, rather than being the standard "good-sounding" intervals. It really throws you off at first, but it's well worth a good listen. (It's six hours long though, so don't listen through it in one sitting.)

https://www.youtube.com/watch?v=vzwgJq9vsDM