Wind and String Octet - a combination of forces, popularized by Franz Schubert (whose Octet is for clarinet, bassoon, horn, violins, viola, cello, and double bass). Paul Hindemith wrote a less well known piece for clarinet, bassoon, horn, violin, two violas, cello and double bass.
Octets in jazz
Jazz ensembles of eight players will frequently be termed an octet. These ensembles may be for any combination of instruments. Ornette Coleman's ensemble for the Free Jazz album (referred to as a double quartet) is one such example.
Saxophonist David Murray leads a famous experimental jazz octet, the David Murray Octet.
Vocal octet
A vocal octet is a choir, or performance by a choir, of eight separate parts, for example, an SSAATTBB (1st & 2nd Soprano, 1st & 2nd Alto, 1st & 2nd Tenor, Baritone, and Bass) choir.