Douglas's last attempt at a piston airliner, the DC-8 Skybus. As development of the Mixmaster, the mechanics of the driveshaft from the engines mounted behind the cockpit, to the rear propellers proved to be the project's Achilles Heel, and as projected costs increased airline interest waned.
If the aircraft had been able to get to the construction phase before it was cancelled, Douglas's arcane numbering allocation system would have renamed the aircraft the DC-8E - so I'm labelling it the DC-8E to avoid confusion.