Convex hulls, Delaunay triangulations, Voronoi diagrams, and proximity graphs by James E. Baker, Isabel F. Cruz, Luis D. Lejter, Giuseppe Liotta, and Roberto Tamassia. Source code is available. The applet calls qhull to build its convex hulls and Steve Fortune 's sweep2 to build its Voronoi diagrams. A forms interface to the same programs is also available. Smoothly maintains the convex hull, Voronoi diagram, and Delaunay triangulation as points are moved, illustrates incremental construction of the Delaunay triangulation, and includes a recorded demo.
Source code is available.
The diagram is updated on the fly while sites or vertices of the unit ball are inserted, deleted, or dragged around. The Voronoi Game by Dennis Shasha. Try to place points to maximize the area of your Voronoi regions. Java not required. Don't give it more than 80 points.