Brown University’s LineoGrammer demonstrates excellent integration with pen gestures to create drawings. Words don’t do it justice - watch the amazing video on YouTube:

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http://www.youtube.com/watch?v=1-Hcz1DKfdo

 

And here’s a link to a PDF with more detail

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http://www.cs.brown.edu/people/acb/papers/lineogrammer-2008.pdf