Its an adjustable angle head for a milling machine (I would guess for a horizontal boring mill) that has seen better days, but it still turns ;-)
The nice thing is that the big cast housing on the rear end, which acts propably as a mounting flange to the machine, can be taken of, then you end up with this very compact adjustable angle drive.
The head is adjustable from 90° all the way to 0°:
And this is how the gear arrangement looks - The central bevel gear is exactly in the swiveling axis of the head:
I intend of building an adapter to mount it to my milling machine, to work on hard to reach areas.