Retro-direct was developed by French inventor Paul de Martin de Viviés
(1833–1911). http://en.wikipedia.org/wiki/Retro-direct I think it was meant for a 60degree seat tube
Building a Retro-Direct Drive Bicycle
Sram has a two speed hub that you have to shift. But I would never give up my MTB gears for anything less that a belt drive with Nuvinci hub.
more odd drives:
This one would be good if it works right, but unless it is in an oil bath, dirt will distroy it.