Fanned frets
On the most guitars, the six strings each have the same length. A fanned fret guitar has six strings with different lengths. This is because strings do have an optimal length. This implies that low strings should be longer than high strings to get the best sound. A similar theorie is used in piano construction.

The first company which applied this to guitars is Novax Guitars. They build acoustic as well as electric guitars. Other guitarbuilders are making guitars in this way too, like Marc Beneteau or Michael Greenfield.

Altough it sometimes looks quite strange on pictures, a fanned fret guitar is as easily playable as a ‘normal’ guitar. The guitar will sound bigger, and in very low tunings there is less trouble because of low tension.
Well known guitar players like Don Ross and Andy McKee play regularly on fanned fret guitars.