http://processingjs.org/

There's also a whole website that allows people to learn programming by using Processing (guessing either a fork or alternative to processingjs or something else) and it's pretty popular. I think Khan Academy had a variation of it too. The canvas in the browser makes a useful tool for Processing to use.

There's also:

http://hello.processing.org/

Which is interactive and has a video lecture attached to it all in-browser.

Now if your concern is processing in production, I cannot comment on that, but for academic use (people learning programming) it's really useful. It is also useful for visual designers so wouldn't surprise me if they use it on the web too.