A metal receptacle installed behind the clothes dryer in rough framing of a new home. The receptacle facilitates the connection and collection of the flex transition hose (the 4" hose between the wall and the dryer) in the cell of the wall instead of on the floor. It is marketed to the builder as a way to save space in the laundry room, reduce the fire hazard by minimizing the potential for the hose to get crushed and saves energy by also minimizing any potential for the hose to get kinked or crushed. A trademarked name of an HVAC product generally installed in new construction by the AC subcontractor.
That dryer fire could of been avoided if the homeowners had a Dryerbox installed.