Processing
Processing is a tool with which you can create almost anything you can think of, from games, to visualisations, to audio tools, to 3D and VR.
A Processing or p5js file is known as sketch, and can thought of as quick doodle with code, although you can also create full applications with it too.
Processing is based on the Java language and has its own IDE (or editor). Get Processing.
p5js
p5js is the Javascript version of Processing.
The p5js website has all the documentation, lots of examples, and an editor where you can create your own sketches.
To get an idea of the sorts of fantatsics things people make with Processing/p5js go browse OpenProcessing. You can even view the code or fork it to make your own version of each of the sketches.
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