This past April, NPR's "All Things Considered" had an April Fools Joke concerning a mythical composer known as Simon Fluegel. You can read about it here ; the point was that Fluegel was exploring a compositional style known as "subminimalism", and had just released a new CD called "B-Flat and other notes", where each composition consisted of a single note played by various instruments.
I thought "Ha ha, very amusing". But now I've discovered Giacinto Scelsi, who actually HAS written a composition called Quattro Pezzi su una nota sola ["Four Pieces on a single note"] (1959). Yes, indeed. The pieces are exactly as advertised. You can even buy the CD at Amazon.com.