It's a Benser Baseplate Adapter (above). It goes on the bottom of a Leica M camera (M1, M2, M3, M4, M6) instead of the regular baseplate and is for attaching 2 extra lenses to the base to carry with you. Designed by Walter Benser, made in Germany, and marketed in the early 1960s. EX, $56, find it on keh.com.
It's an OROLF lens turret with handle. Mounts to a Leica M2 or M3 camera and holds three screw-mount lenses for a faster lens exchange. Has its own baseplate which fits onto the bottom of the camera. Produced for one year in 1960, with production numbers at 250 or less. EX+, $2,029, find it on keh.com.