Sheldon Pacotti, writer of the original Deus Ex games and indie developer in his own right, created Game Blocks, an open-source library for making games, for the students in his video game writing course at the University of Texas. Game Blocks is designed to help novice developers craft their stories, animations and physics effects with a simple, snap-to interface, as demonstrated above.
Game Blocks is able to compile platformers, adventure games, simulation games and arcade shooters for PC and Mac, and makes it easy to organize dialogue and story. Best of all, it's completely free. Anyone interested in messing around with game design or interactive storytelling, download Game Blocks directly from Pacotti's New Life Interactive.