It is intended to be used for motion picture film in a projection
booth.  You put a full 2000' reel (just removed from the lower
magazine of the projector) on the left spindle, an empty one on
the right spindle, and move the lever on the top to the left and
the thing will rewind the film for you.  There is an auto-stop
mechanism which wlll stop the motor when the left-hand reel stops
spinning.  While the previous reel is rewinding, you thread the
next reel into the projector (meanwhile,the film continues on the
second projector).

Many older theatres have these and some still use them.  You can
actually buy a brand-new one (at an insane price) from Goldberg.

The concept is nice, but the motor only runs at a single speed and
these things tend to cinch the film at startup, causing scratches.
These are largely useless in multiplexes, which invariably use
platter-type projection system (where all the reels of the film
are spliced into a continuous strand and the film rewinds as it
plays-- think of an 8-track tape or broadcast cartridge; most
platters aren't endless loops, but they do feed from the center of
the roll).