The Kelstone 9-string instrument can be played using both hands, like a piano. 2 / 20. Kelstone weighs 18.29 pounds, is 42.5-inches long and has adjustable screws at the nut. 3 / 20.

Calhoun, co-founder of Rockbridge Guitar, is hoping to change that with TinkerTar, a new, scaled-down version of the instrument that has only one string instead of six to make it more accessible ...