Wikipedia
Octophone
The octophone (or octofone) is a stringed musical instrument related to the mandola family resembling an octave mandolin. It was marketed by Regal Musical Instrument Company, who introduced it 21 January 1928, as an "eight-purpose instrument".
The name "Octophone" came from the idea that the instrument could take on the "tone combinations" of eight instruments, the tenor guitar, tenor banjo, ukulele, taro patch, tiple, mandolin, mandola and mandocello. Changing from one instrument to another was a matter of changing the tuning. The instrument came with an instruction book that told owners "how to use, how to tune and how to play" the instrument