SC-47A
This model was modified for Search and Rescue use by the U.S. Air Force and Coast Guard. It was based on islands and airbases located close to the sea, from which it would fly out over to search for downed airmen, shipwrecked sailors, and more. Though it could not land on the water, the SC-47A often dropped life rafts and supplies so that the castaways could survive until rescue seaplane or ship could pick them up.
Li-2
The Li-2 was a license-built variant of the C-47, meaning it was built in Russia by Lisunov by permission of Douglas and U.S government. It was used as a transport aircraft, much like its American counterpart. However, the Li-2 flew with shutters over its engines to cope with the extreme cold of its homeland, as well as a dorsal machine gun turret to defend against German fighter attacks.
XCG-17
Here's a weird one for you. Throughout the Second World War, the American Army Air Force used gliders to insert troops silently and quickly behind enemy lines. To this end, Douglas removed a C-47 from the production line, removed its engines, and placed aerodynamic cones over their mountings. Thus, the XCG-17 was born. Though it performed well in tests, the XCG was deemed unecessary by the AAF and forgotten.