Now, if they added a server-side API to Processing, that might be interesting...

I don't get this. It's a javascript library--you can host it wherever you like.

AppJet gives you an in-browser editor to edit your processing.js app, you can instantly view the results, and then you can choose a subdomain for your creation.

This is in the spirit of Processing, which itself is all about by-passing unneeded complexity to make cool stuff.

Right, but you can also do the same with vim and any web host with shell access. I guess it just seems to me like a solution to a nonexistent problem.

When your non-hacker-but-smart friends come up to you all bright-eyed and say "Hey, a cool graphics gizmo! I want to make one of those!", what do you say? Learn vim? And unix, and web server configuration, and get out your credit card and fill out a long web-form? You must be a hit at parties.

Even (or especially?) for hackers, it's fun to have an environment to play around in without a lot of set-up. Granted, a lot of existing in-browser IDEs don't live up to their potential, but AppJet has a chance to be different in this regard.

As easy-to-use libraries and frameworks like Processing and AppJet catch on, I think they will be of use to a lot of people who don't already have a shell window open to a web server somewhere.

Aside from the fact you don't need a web server to use a JavaScript library...

You do if you want to share something you create with other people.