Ben Dove’s String Thing is a cello-like instrument with four metal bars that can be struck or stroked. Like a fretless instrument, pitch is continuous.

Building String Thing: Laser Pointers and Vibrating Rods: What’s great about the String Thing is two-fold: first, it’s an ingenious design, and second, Ben rigorously documents how he did it, including some false starts. The steel rods are a “stroke” of genius: using magnets, the rods “vibrate” as you play them for physical feedback, while a sophisticated combination of laser pointers and webcams calculate your finger position. There’s plenty of expressive control, as well, though the limited Max/MSP-based demo video doesn’t quite do the sophistication of the controller justice. Ben has an impressive resume of other projects, as well.

See also:
Haken Audio’s Continuum controller, which also works from the premise of providing continuous pitch control instead of the limitations of a keyboard. Via Regine / WWMNA.