Pencil Code
http://pencilcode.net/

Learn professional programming languages using an editor that lets you work in either blocks or text. Create art, music, games, and stories. Or invent a program that will change the world. Pencil Code is a collaborative programming site for drawing art, playing music, and creating games. It is also a place to experiment with mathematical functions, geometry, graphing, webpages, simulations, and algorithms. Programs are open for all to see and copy. This will be added to Script Resources Subject Tracer™. This will be added to World Wide Web Reference Subject Tracer™. This will be added to Business Intelligence Resources Subject Tracer™. This will be added to Entrepreneurial Resources Subject Tracer™. This will be added to the tools section of Research Resources Subject Tracer™.