JFLAP, JAWAA, jeLLRap -- Visual and Interactive Tools - Tools (Java programs) for visualizing and interacting with theoretical computer science concepts. JAWAA is a tool for creating algorithm animations on the web.
Leonardo - An integrated C programming environment for reversible execution and logic-based software visualization developed at the University of Rome "La Sapienza".
LYDIAN - Simulation and visualization environment for distributed algorithms that provides students with an experimental environment to test and visualize the behaviour of distributed algorithms.
Opsis - A Java applet designed to teach binary search tree algorithms. It is unique in the way it combines programming, proof, and animation to enhance the learning experience.
Sort Algorithms Visualizer - Applet and web site for teaching sort algorithms. Includes animation of 11 algorithms and some in-depth studies.
3 Sorts of Sort CAL Package - Several sorting algorithms explained using a nice playing card based interface.