Blockly
The web-based visual programming editor
...Custom blocks may be created to connect to your own application. Blockly in a browser allows web pages to include a visual code editor for any of Blockly's five supported programming languages, or your own. Blockly plugins are self-contained pieces of code that add functionality to Blockly. Blockly codelabs provide step-by-step instructions on how to use and customize Blockly. From a user's perspective, Blockly is an intuitive, visual way to build code. From a developer's perspective, Blockly is a ready-made UI for creating a visual language that emits syntactically correct user-generated code. ...