This set of widgets and context-sensitive gestures was designed to make it easy to apply 3D transformations in pen-based 3D interaction systems. The prototype was implemented in ShapeShop, and is described in the Eurographics 2008 paper "Sketching and Composing Widgets for 3D Manipulation". More details are available here:
dgp.toronto.edu/~rms/pubs/SketchWidgetsEG08.html

If you want to try it out, download ShapeShop for free at shapeshop3d.com