After long pondering after my separation from my wife, I was inspired by scratchgolf's posting at http://www.talkclassical.com/35120-schoenberg-experiment.html and was very impressed. Schoenberg is not an easy composer to wade through singularly for a whole month.
In this vein, I have decided...
Post world war 2, it is basically music that features repetition and iteration. Here is an example. A piece by Morton Feldman, his piano and string quartet (1985), it's about an hour and twenty minutes long.