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GEUP - Interactive Geometry software.
GEUP is an interactive geometry tool. Lets you dynamically explore Mathematics, build mathematical models of real world or create interactive mathematics presentations.
http://www.geup.net
Qhull for convex hulls, etc.
Qhull for computing the convex hull, Delaunay triangulation, Voronoi diagram, and halfspace intersection about a point.
http://www.qhull.org