The Free On-line Dictionary of Computing (30 December 2018):

Sketchpad

   A program that allowed users to draw on a screen with a light
   pen.  It supported constraints (e.g. drawing a constrained
   ellipse produced a circle).  It also had some computer aided
   design features (e.g. computing loads on beams).

   Sketchpad was the subject of Ivan E. Sutherland's 1963 MIT
   PhD thesis, which opened the field of computer graphics.  It
   was the progenitor of computer drawing packages like MacDraw
   or Adobe Illustrator.  There is a film of Sketchpad in
   action.

   It solved constraints using value inference and introduced
   the "ring" list structure.

   ["Sketchpad: A Man-Machine Graphical Communication System",
   I.e. Sutherland, MIT Lincoln Lab, TR 296 (Jan 1963)].

   [Sammet 1969, p. 678].

   (1995-02-14)