1. Contra-bassoon: This is a larger and lower-pitched version of the bassoon. It is tuned an octave lower than the regular bassoon.
2. Contra-alto clarinet: This clarinet is pitched one octave lower than the alto clarinet and two octaves lower than the standard B-flat clarinet.
3. Contra-tuba: The contra-tuba, also known as a contrabass tuba or C tuba, is the largest and lowest-pitched member of the tuba family. It is pitched one octave lower than the standard B-flat tuba.
4. Contra-bass: The contra-bass, or double bass, is the largest member of the string family. It is tuned an octave lower than the cello.
5. Contra-trombone: This rare type of trombone is tuned one octave lower than the tenor trombone. It is not commonly found in modern orchestras or bands but can be used in larger ensembles for additional depth.
6. Contra-guitar: A modified version of the acoustic guitar that is tuned an octave lower than the standard guitar. It produces a lower and fuller sound.
These contra-instruments are often utilized to add depth, warmth, and a stronger low-end presence to an ensemble's overall sound. They can also be used to add contrast, emphasizing specific melodic lines or providing a solid harmonic foundation.