Crazy J isn't the guy you used to buy from. It's a killer guitar robot built by students at the Georgia Institute of technology. Like any good robotic guitar system, it sounds surprisingly alive and fresh.
The system uses small pushers to hold down the strings and pluck or strum based on MIDI data. As Musicthing pointed out, this is very similar to the system used to animate Jack White of the White Stripes and his robotic drummer, Meg 2005.