Leonardo da Vinci sketched an invention dubbed the viola organista more than 500 years ago, though apparently he never built one. Over the years, various versions of this "bowed keyboard" were built, mostly based on da Vinci's sketch.
This year, Polish pianist Sławomir Zubrzycki unveiled his own version of the instrument -- and played it beautifully. Have a look:
But while that video is lovely, it doesn't explain much of what we're hearing, or how it came about. Here's a ten-minute documentary (with English subtitles) explaining how and why Zubrzycki built his viola organista. (If the subtitles don't pop up for you, hit the "CC" button on the YouTube player.)