Have a look at the OAR ascender/descender designed and built by Gordon Svedberg. The prototype OAR doesn't have the finesse of the Unicender but you can see the potential.
Moss TreeClimber tested the OAR on a doubled rope set-up but it would be interesting to see how the device performs on single rope.Most climbers using the Unicender (in New Zealand) opt for SRT but it can be used in a similar way to the OAR.
Thanks to Drew Bristow for this lead
