The Ondes Martenot (pronounced "ond marteno") dates back to the twenties. Its distinctive, ghostly sound is attributed to the vacuum tubes used to produce oscillating frequencies. It can be played just using the keyboard, or by placing a metal conductive ring around the right index finger and sliding it along a band. The location of the ring corresponds with the note on the keyboard. While the right hand controls pitch, the left hand controls volume by pushing a pressure-sensitive lever. In playing technique, this makes it very similar to a theremin (another 1920's electronic instrument). While remaining obscure, dozens of pieces have been written for it by modern classical composers over the years. I saw a Tom Waits Opera a couple years ago which included this (along with the Glass Armonica) in the orchestra, and I was utterly spellbound by its ethereal quality. More recently, anyone who's seen There Will Be Blood heard the Ondes Martenot prominently in the ten-minute wordless opening sequence. It was composed by Jonny Greenwood (of Radiohead), easily the most recognized contemporary promoter of the instrument. Here's the piece, titled "Smear". It isn't included on the soundtrack CD (also excellent) because it was written and recorded before the film was made. Greenwood also contracted this ersatz-martenot keyboard controller to be designed and built for him, now available to the public. (one more note... this instrument is often confused with the electro-theremin, most famously used in Brian Wilson's "Good Vibrations" and best described as an idiot-proof theremin, but both the martenot and the traditional theremin have more nuance).