This is a Dondi drain / ditch cleaner.
https://www.dondinet.it/en/ditcher/central-excavation/mono-wheel/

It can be used directly behind the tractor or offset on the 2.4m mechanical arm (included)
https://www.dondinet.it/en/ditcher/side-excavation/with-wide-side-displacement/

From the website:

Mono-wheel central excavation ditcher to excavate ditches with a maximum depth of 35 to 78 cm and wall angle of 30°. The soil is only distributed on the right side of the ditch.

Typically used to excavate temporary drains intended for surface water drainage or small irrigation ditches.

Rare to find one of these, ideal for use on Peat ground.
Looks to have done very little work.
Hamilton yard.