Viper - Visual Pascal Interpreter

I saw VIPER for the first time when Codility was taking its current shape. I was seriously impressed and inspired. VIPER is a full-fledged compiler and interpreter of Pascal that runs as Java applet entirely in a browser. On top of that VIPER contains a debugger with excellent datastructures visualization capabilities, in some aspects well surpassing those of DDD. VIPER was created as a teaching tool at Warsaw University Institute of Computer Science by Piotr Chrząstowski-Wachtel, Anna Niewiarowska and Michał Adamaszek. VIPER's main goal was to aid development and understanding of solution to fundamental programming exercises. In this context the visualization capabilities come in extremely handy, especially when linked structures (lists, trees) are involved. VIPER comes pre-packaged with a set of solutions to fundamental programming exercises (longest common subsequence, BST insertion, three-color flag, maximum subsequence sum, binary search, list merge etc.). See for yourself.