Wikipedia
CodeSkulptor
CodeSkulptor is an interactive, web-based Python programming environment that allows Python code to be run in a web browser. The application was developed by Scott Rixner, a professor of computer science at Rice University. Its features include visualization of program execution; the ability to conveniently store, edit, and share code online with other users; and cogent error messages that are helpful for debugging code.
Currently, CodeSkulptor must be run in Chrome 18+, Firefox 11+, or Safari 6+ for full functionality.
CodeSkulptor is currently used by students at Rice, as well as in Coursera programming courses.