The viocta is an eight-stringed instrument closely resembling a violin, invented by the Dutch musician Willem Wolthuis in 1971. The neck of the instrument is approximately an inch wider than that of a violin, and somewhat lengthened to support the eight strings. The instrument also uses an aluminum tailpiece, since the large number of strings makes the instrument subject to a lot of strain.

The instrument has four violin strings and four viola strings. The violin strings are tuned conventionally as G, D, A (440 Hz), and E. The viola strings are tuned to D-flat, A-flat, E-flat, and B-flat; a half step above normal. The strings are paired as follows (from left to right): D-flat - G, A-flat - D, E-flat - A, and B-flat - E. (As implied by this order, the instrument is tuned in perfect fourths.)

The instrument allows the possibility of playing eight-part chords and clusters, four-part harmonics, overall goofy colors, and abstract sound effects.
From: The Complete Encyclopedia of Musical Instruments by Bert Oling and Heinz Wallisch