JD and likely Bushog have offset versions.

It's basically a 15 ft batwing with only one of the wings and a counterweight box in place of the other.

Might not be what you are referring too though?  Still would need tractor on the slope for wider ditches. Mostly used by highway departments to reach under trees or other obstructions.

Images courtesy of machine finder.

(cx15 (Medium) (full).jpg)

(cx15 2 (Medium) (full).jpg)

cx15 (Medium) (full).jpg (188KB - 1 downloads)

cx15 2 (Medium) (full).jpg (221KB - 1 downloads)