Blockly, a graphical programming language.
http://code.google.com/p/google-blockly/
Neil Fraser

Server:
Despite the fact that Blockly has no server-side code whatsoever, it must be
served from an http:// or https:// server for security reasons (a local file://
protocol won't work).

Editor:
To run the editor, load blockFactory.html in a browser.

Tests:
To run the unit tests, load blockly_test.html in a browser.