There are six instruments in the oboe family that are still at least somewhat in use today. All of these instruments are woodwinds and double-reeds.
Musette
The musette, or piccolo oboe, is the smallest and highest-pitched member of the oboe family. It is in the key of either Eb or F and is comparable to the Eb clarinet. Music for the musette is modern or for chamber double-reed groups. They are made with the same full conservatory system that oboes have, and they are a more rare member of the family.
Oboe
The oboe is the most common in the oboe family. It is pitched at C and plays a vital solo role in the orchestra as well as having the task of tuning the orchestra before a performance. Oboes are about 26 inches long and their range is from Bb3 to A6. There is more repertoire for the oboe than the musette including concertos and chamber music dating back to the 18th century.
Oboe D’amore
The oboe d’amore is larger than the oboe and has a mezzo-soprano range. Its concert pitch range is G#3 to D#6, and it is pitched at A. It was more popular in the Baroque Era and then again in the Impressionist Era. Most repertoire for the oboe d’amore is from these times.
English Horn
The english horn, or cor anglais, is second to the oboe as the most common instrument in the family. The english horn is pitched in F and is lower than the oboe with a concert pitch range of E3 to C6. It could be considered the alto instrument in the family. Oftentimes, the english horn is played as the secondary instrument of the second oboist and the musician will switch between them in performance as needed. This instrument has few solo works, but is more well known in chamber music and orchestral excerpts.
Bass Oboe
The bass oboe, or baritone oboe, is confusingly sometimes also referred to as the tenor oboe because of its range. It is twice the size of the oboe and its music is written in treble clef, but the true notes played are an octave lower. Its range is a B2 to F#5 in concert pitch. Bass oboe has some notable excerpts from orchestral music but solo repertoire for it is almost non-existent.
Heckelphone
The heckelphone is the lowest member of the oboe family. It is also pitched an octave lower than the oboe, like the bass oboe, but its range is extended a semitone lower than the bass oboe (A2 to F#5) and it has a wider bore. The heckelphone is heavy and rests on a peg on the floor when played. Richard Wagner came up with the idea of the heckelphone which was carried out by Wilhelm Heckel in the early 20th century making it the newest member of the oboe family with less than two hundred instruments ever made.
Had you heard of all these instruments before?
Also, one baritone oboe (“baritone sax-oboe”) in the key or Eb exists, made by Cabart.
Unique example. Same range as an alto saxophone. See image on http://www.oboes.us