Eight-string guitar

An eight-string guitar is a guitar with two more strings than the usual six, or one more than the Russian guitar's seven. Eight-string guitars are less common than six- and seven-string guitars, but they are used by a few classical, jazz, and metal guitarists. The eight-string guitar allows a wider tonal range, or non-standard tunings (such as major-thirds tuning), or both.

Agile Intrepid
Homemade fretless guitar based on Jackson Rhoads
Eight-string multi-scale acoustic guitar by luthier Patrick Hawley of Ottawa, Ontario

Various non-standard guitars were made in the 19th century, including eight-string guitars played by Italians Giulio Regondi and Luigi Legnani.[1]

Eight-string guitars gained popularity among metal bands, largely inspired by Swedish progressive metal band Meshuggah (formed in 1987).