Scratch

Scratch is a new programming language that makes it easy to create your own interactive stories, animations, games, music, and art -- and share your creations on the web ....designed to help young people (ages 8+) develop 21st century learning skills. As they create Scratch projects, young people learn important mathematical and computational ideas, while also gaining a deeper understanding of the process of design.
Scratch is available free of charge, go to Download.
Currently available for Mac OSX and Windows (system requirements)