Nevborn Sleipner 8-String Guitars
Sleipner is the name of Norse God Odin's 8-legged horse, making it a good name for a scandanavian 8-stringed guitar. Fredrik Nevborn is a luthier (in Sweden I think) who builds custom guitars by special order. He has two varieties of 8-string guitars, the Sleipner I which is designed to be tuned A D G C F Bb D G (low to high), and the Sleipner XL, which is tuned F Bb Eb Ab Db Gb Bb Eb.
The Sleipner XL is used by Fredrik Thordendahl of Meshuggah. The string length is longer than that of a standard electric guitar, giving it a clear, deep sound with lots of overtones when played "clean" and it has a thunderous, gutteral low end when played with distortion. The price tag is steep at $3000 ("prices may vary due to your own setup"), but they are hand-built to order, and Nevborn will work with you to create a custom instrument.