An Australian company called Misa has built a digital guitar that replaces the strings of a regular guitar with a touchscreen. It has 144 buttons on the neck for generating MIDI notes, which are then modified by pressure and position on the touchpad.
"In electronic music, the timbre (or colour) of the sound can be morphed in an infinite number of ways", says the company behind it. "For a guitar to accommodate this, the right hand needs more control than just plucking strings. You need to be able to control elements of the sound, such as sustain, pitch, filter cutoffs, contour or any other synthesizer parameter, in a way that has no physical constraints".
The device runs Linux kernel 2.6.31 and has MIDI-out and Ethernet connectivity as well as an onboard SSH server. For it to generate sound, you'll need to plug it into a MIDI sound module and hook up a synth of some sort, but once you've done that you can confiugure the touchscreen to morph different aspects of the sound.
The overall effect is a bit like a regular electric guitar put through a Kaoss pad, something that has been done before. It's a little more elegant than those hacks, though, and given it runs Linux, you could even play a bit of Tux Racer while your regular guitarist is tuning up.
There's no pricing yet, but there is a waiting list for if you're desperate to get your hands on the guitar.