Leo and the T-Rex is an educational application for all ages. The essential time filler for those crazy moments in the classroom when a teacher doesn't know what to do but wishes they could impress the administrator that just happened to walk in the classroom. The application includes an augmented reality simulation of a T-Rex walk cycle and roar. This has been tested and certified cool by students from k-12 in the lovely mountain community of Tehachapi, California. The application also includes a short bilingual anatomy lesson for the k-3 students. For students of all ages there are appropriate video links to great educational content such as the building of the T-Rex for the Jurassic Park movie series, how to make an origami T-Rex, speed drawings, and coloring activities from the application's home website. Also included are links to the source code of the application because the project is Open Source! This means that the code is available for learning or sharing via a Creative Commons license. The code itself builds upon code from cocoacoder.org.