All you need to get started is your browser, as their browser based IDE includes syntax highlighting, preview and publishing features. Any app you write can be hosted for free on their site and a 10MB persistent storage is also provided if your application requires it.
As I browsed through the AppJet site, I decided to code a very simple app to see how long it would take, just to test out AppJet. ;) True enough, after about 30 minutes, I managed to finish my simple web proxy. Much of my time was spent on reading the documentation and searching for relevant functions rather than coding.
A simple proxy uses the wget function to download the HTML of remote sites and spits that HTML back out into a div. It is very basic and will not retrieve anything other than text. If you happen to see images, you're downloading them from the originating server and not from AppJet.
After my short and pleasant experience with AppJet, I'm wondering if I should port tk Google Charter over. It'll be neat to have data storage so that I can implement a last 5 charts feature or something similar.