Wikipedia
The octavin is a woodwind instrument with a conical bore and a single reed. As such it resembles a saxophone, and its range is similar to that of a soprano saxophone, but the octavin differs in three respects: first, its conical bore has a smaller taper than that of a saxophone; second, its body is made of wood, rather than metal; third, its usual shape is similar to that of a bassoon, having two parallel straight sections joined at the bottom, with the mouthpiece attached to the top of one section and a metal bell to the top of the other. (A few straight octavins exist, having a wooden bell; in this configuration it resembles a tarogato but has a smaller taper.) The instrument was produced in B♭ and C. One writer (Altenberg) mentions a bass octavin but no such instrument is known to have been produced. The (written) range of the octavin is from G♯ to G.
While invention of the octavin around 1893 is sometimes attributed to Julius Jehring, Oskar Adler and Hermann Jordan of Markneukirchen patented it.
The octavin never caught on and is an extremely rare instrument, though the American composer Jeff Britting (b. 1957) has composed a sonatina for octavin.