I am interested to know your best tool for rapid yet maintainable rich web app development. I know few tools and would like to poll on them.<p>1. Ext JS (http://www.sencha.com/products/extjs/)<p>2. qooXdoo (http://qooxdoo.org/)<p>3. Cappuccino (http://cappuccino.org/)<p>4. HTML5 and CSS3
Surprised Backbone.js(<a href="http://documentcloud.github.com/backbone/" rel="nofollow">http://documentcloud.github.com/backbone/</a>) didn't make the list.
I've built a couple of applications with Qooxdoo, and found it fairly simple, especially for the one like me, who was never programming any serious JS before. I still dislike javascript, but that's a different story :)
Sencha is great. I wrote demo apps for Sencha associations, grids, MVC, REST, XTemplates, etc.<p><a href="http://github.com/sixarm" rel="nofollow">http://github.com/sixarm</a><p>Then search for "sixarm_sencha"
If you are looking for fast end to end modern web apps you should look at wavemaker, VMWare picked them up. For just knocking out quick REST / js CRUD apps they are in a league of there own.