The Synthaxe Drumitar is an instrument created by "Future Man", or Roy Wooten of Béla Fleck and the Flecktones. The Drumitar comprises piezo elements mounted in a guitar shaped body, connected by cable to assorted MIDI devices including samplers and drum machines. The instrument is one of a kind, and it was originally modified from a SynthAxe previously owned by jazz musician Lee Ritenour. 
The Zendrum is a similar instrument that is commercially available.