Name: Double contrabass flute

Also known as: octabass flute / subcontrabass flute
Invented by: Dutch instrument maker Jelle Hogenhuis
External Links: https://en.wikipedia.org/wiki/Double_contrabass_flute
https://bandestration.com/tag/double-contrabass-flute/
https://www.contraflute.com/about-the-contraflutes/ 

Disambiguation: Flute, Bass flute, Contrabass Flute
Description: This wind instrument is the largest and lowest pitched metal flute which is pitched in the key of C. It has a relatively powerful tone with three octaves below the concert flute.