p5js is a creative coding tool and is the newer, web-based, Javascript version of Processing. It is great for creative coding.
The OpenProcessing site is a gallery of the amazing projects that have been made with Processing and p5js.
(Slightly confusingly, p5js is the modern Javascript version of Processing. Processing itself is java-based)
Not only is this site inspirational, you can also view the source code, and remix any project you like to develop your own version.
Lauren both introduces the making of p5js and demonstrates how totally cool p5js is, highlighting some of it best features.
The source code for COW IN SPACE is available here.
Great collection of code examples showing what you can do with p5js
Another site where you can explore other peoples' excellent p5js sketches.