Gato the Graph Animation Toolbox Gato, the Graph Animation Toolbox http://gato.sf.net by Alexander Schliep and Winfried Hochstaettler, is a LGPL-licensed Python application which animates algorithms on graphs. It uses Tkinter and runs on Unix, MacOS X, Linux and Windows. It is primarily a teaching tool, but can also be useful in research on algorithm design and engineering, for example by demonstrating effects of heuristics. It is used in CATBox (Springer 2010, see authors' website http://schliep.org/CATBox) by Winfried Hochstaettler and Alexander Schliep. CATBox is a textbook on combinatorial optimization on graphs (traversals, minimal spanning trees, shortest paths, maximum flows, min-cost flows, cardinality and weighted matching) which uses Gato to provide interactive animations and exercises for all algorithms. A screencast is at: http://biomaps.rutgers.edu/~schliep/CATBox/Dijkstra.swf Gato and CATBox has been used in university classrooms for several years by us and colleagues on several continents at the undergraduate and graduate level. Winfried Hochstaettler is a professor in mathematics at the FernUniversitaet Hagen, Germany and Alexander Schliep is an associate professor in computer science and quantitative biology at Rutgers University.