What is your best rich web app development tool?

Surprised Backbone.js(http://documentcloud.github.com/backbone/) didn't make the list.

I just had heard the name. I didn't know it's for frontend development.

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.

http://github.com/sixarm

Then search for "sixarm_sencha"

I am already using Sencha Touch so I believe Ext JS would do the job but then their commercial license would need to be bought. MIT license is great.

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.

http://sproutcore.com/

#4 for me, although jQuery is what is really doing all the heavy lifting.

+1 to that.