Perhaps not the oddest moped I've ever come across- but then, how many other three-wheeled mopeds can you name? I found this one at a Norwegian motorcycle fan site. The Ariel name is curious; the 'ped bears little resemblance to the original Ariel, other than that both are odd machines dreamed up by a company management that was often said to be completely out of touch with the motorcycle riders of Great Britain!
There's an excellent history of the bike at this web site, from which I quote:
With a conventional (rigid) tricycle, steering, as for a sidecar outfit, is by turning the handlebars either left or right. However, the Ariel-3 is meant to be ridden by leaning on bends, as for a conventional moped and for this type of riding, turning the bars as well is an unnatural act. Yet, because the Ariel-3 is a tricycle, albeit with the rear part hinged, leaning over on its own is not enough to initiate cornering by itself and it has to be steered as well, and this is done by steering the rear wheels to push the vehicle into a turn. The two torsion rods are adjusted up so that as the front leans further over, the rear wheels steer a tighter turn and provided that the adjustment is correct this all happens smoothly and gives the same results as would be expected with a normal bike. However, with the rods out of adjustment what happens is that when the rider first starts to lean nothing seems to happen and they continue straight on. Panic then sets in and the rider leans further, at which point the slack in the rods gets taken up and the Ariel-3, seemingly with a mind of its own, shoots into the bend far sharper than the rider intended.
Perhaps this is why the bike was not a resounding success. Then again, the typical European moped buye of that era was a 14 or 15 year old male who can't wait to own his first motorcycle, and the Ariel 3 didn't exactly conjure up images of racing Triumphs and BSAs. It remains an oddity in the history of mopeds, but like all oddities, that's a big part of its charm.