File this under archaic devices I had no idea existed. Here’s a once in a lifetime opportunity to own a mint-condition Keaton Music Typewriter. Patented in the early 1930s, there are only a dozen or so in existence. What does it do? Exactly what you think it does. Via musicprintinghistory.org:
The Keaton Music Typewriter was first patented in 1936 (14 keys) by Robert H. Keaton from San Francisco, California. Another patent was taken out in 1953 (33 keys) which included improvements to the machine. The machine types on a sheet of paper lying flat under the typing mechanism. There are several Keaton music typewriters thought to be in existence in museums and private collections. It was marketed in the 1950s and sold for around $225. The typewriter made it easier for publishers, educators, and other musicians to produce music copies in quantity. Composers, however, preferred to write the music out by hand.