DreamSlider from Jean-Marc Gobillard , he says stand up for your folder!
He even search for a patent for the method of doing it. Standing up pedaling.
He even made a MicroSlider in case you find 12" wheels to be too big?A pedaling method and device for a user in standing position. The device includes a drive shaft whereof the rotation about its axis is coupled with the rotation of two right and left pedals.
The vertical oscillation of the center of gravity of a user in standing position is reduced compared to a conventional pedal assembly.
If you speak French then read here too
5 Videos at his youtube page.
I have not found any good stills on it though. you maybe can see how small it is here but the videos and pdf shows it swishing by. Why doesn't he set up a free blog or something with pictures and specifications? ok it is a prototype still.
Here is picture of Dream Slider