This came to me as a surprise as I ignored this when I first saw it as a java platform thing. Recently, while going through some of the new Flash frameworks for fireworks :) and magic, it hit me again. And this time I made sure to check it out. To my surprise its a beast wrapped up in a beautiful wrapper. Having all the potentials of JAVA, Processing is a new kind of language(or may be Sripting language). Internally it compiles back to Java and can be used along with any front-end Java application. The real magic is its speed, and the fireworks it does. A very simple API and out of the box compilation support. It provides a lot of things out of the box,which is best for any newbe to Java platform. It comes with its own IDE,though one can choose to use Eclipse if she/he wants to. Compilation is instant and right upfront. When talking about packaging,it does nice job of compiling to all the platforms,Windows,Linux and Mac from Windows itself. The size of the compiled files(java applets) are as small as SWFs.
For a Flash developer this is a real option to try out Java this way. For the scripting Processing provides will make the Flash developer feel right at home. A lot of similarities All most everything is similar except for the APIs,which will make one think as if one is working in a Flash-platform framework. One gets animations, mouse actions and stage like behaviors from the application too :)
I would say, a must try for all the Flash and JAVA guys out there.