People ask about this instrument. Generically, it's a guitar-bodied octave mandolin. Specifically, it is one of Austin Clark's creations. He lives and works in Boise, ID. His mandolins have been featured as prizes for the mandolin contest at the Walnut Valley Festival the last several years.
I got interested in this style of instrument after watching videos of Sarah Jarosz, Sierra Hull, John Mailander and others playing one. Its sound is kind of like an acoustic guitar being run through a chorus pedal, but distinctly different than a twelve-string guitar.
I've had this instrument for less than two years. It is tuned one octave below a regular mandolin, placing it a fifth higher than a mandocello and a fifth lower than a mandola. It has the same range as a guitar tuned to standard and capoed at the third fret.
The scale is long enough that standard closed chord positions are sometimes impossible, but the nice bass and middle available from the open lower strings makes you wonder why you'd even try.