Here's an interesting sculling oar, developed by Guy Capra in Toulon. His blog is in French, so I have probably got this wrong, but Guy points out that sculling over the transom is a difficult skill to learn because it involves a counter-intuitive figure-of-eight movement of the handle.His design, dubbed godyoto (godille is French for stern oar), has a crank in it that forces the blade to turn in the right direction when you pull the handle. Traditional Chinese yulohs are bent, like the godyoto, but don't have the crank. The pictures make it clearer. And the video makes it clear it works.
I tried over-the-stern sculling in Nessy a couple of weeks back, using a long oar I bought off eBay, and made little headway though I did manage to go forwards rather than in circles. If the godyoto really does work it would be brilliant for sculling round harbours.
As a bonus, the crank splits the oar in half for easy stowing in the boat when not in use.
(Thanks to Duckworks for the heads-up)