The Dual Drive hub has been around for quite a while now. It's a popular choice for small wheel bikes, like folders. My Friday has been running such a hub since day one - with no problems. It has a gear range of approx. 19-100 inches.
The hub provides three different gear ranges and combined with a 9-speed cassette, gives three different "sets" of nine gears. As mentioned, the bike needs only a single chainring and no front changer.
One of the advantages of the Dual Drive is that it allows one to switch between the three gear ranges at any time - even while stopped.
The hub does require a few non-standard parts. Anyone riding away from home should consider bringing along spares - a shift pin, locking washers for the axle bolts and maybe even a spare click-box.