Blockly

Website: developers.google.com/blockly

Blockly is a client-side library for the programming language JavaScript for creating block-based visual programming languages (VPLs) and editors.

A project of Google, it is free and open-source software released under the Apache License 2.0. It typically runs in a web browser, and visually resembles the language Scratch.

Blockly uses visual blocks that link together to make writing code easier, and can generate code in JavaScript, Lua, Dart, Python, or PHP.

It can also be customized to generate code in any textual programming language.