Visual Ajax Studio is a free, open-source app that helps programmers to quickly and easily create user interfaces in AJAX. At the same time, it helps novice users to begin learning about this method of development.
Visual Ajax Studio runs from your default web browser, so we could call it a web application - but it also runs locally. It has a pleasant look and it's not difficult to find the options that you need.
And did we mention that it's free and open-source? There shouldn't be anything holding you back from giving this service a try.