The Stretch-A-Sketch pen-based drawing program combines recognition of hand-drawn glyphs with constraint based maintenance of spatial relations. The recognition program identifies hand drawn glyphs, spatial relations between them, and higher-level configurations, such as graph and tree diagrams and floorplan bubble diagrams. Stretch-A-Sketch then maintains the essential relations in these configurations as the user edits the diagram.
1994 Stretch-A-Sketch, a dynamic diagrammer, Gross, M.D., in A. Ambler, ed., IEEE Symposium on Visual Languages 1994, pp. 232-238. [pdf]