This is a pen holder designed for a Norland Research Calculator Controlled Robot: http://www.smallrobot.com/
It is sized to work with a standard full-size Crayola marker ~14.5mm diameter. There is a bridge between the clamp and the base which acts as a spring hinge to keep pen pressure consistent across bumps and dips.
~15 min print on MakerBot #322
Skein, (or use my gcode)
Use it in conjunction with a robot to draw things. Draw shapes on large sheets of paper. Circles are easy
Or use it as a pen holder wherever you need to hold a pen.