I've been working with ExtJS lately, and I must say I am highly impressed. For those of you not familiar with ExtJS (Ext), Ext is a crossbrowser javascript framework that allows for the creation of RIA (Rich Internet Applications).
Ext uses the latest and greatest web 2.0 methods, such as ajax, which has built in parsers for JSON, XML, text and possibly some other formats. Ext allows for the creation of desktop looking interfaces with just som simple notation(Ext is probably not the first project to do this)...this in my opinion is one of the greatest things Ext has to offer. The simple notation way of creating these interfaces allows for rapid deployment of interfaces, and takes the GUI creation out of the hands of the developer, and allows the developer to focus on getting the data to the front end.
Alot of chatter has been generated in the past couple of months on the decision to change the licensing model. The most current version of Ext uses the GPL 3.0 model in my opinion it may have not been the greatest of choices for a license however it still allows you to create open source applications. And if you want to build an application that you will be selling for $ you can purchase a license which will ultimately help support the project and only make it better.
There is one negative aspect to Ext, the documentation....yes all the information you need is there and they even give some basic code in the documentation however in my opinion the examples of interfaces/widgets are all given in the notation format of creating objects however the examples in the docs all give examples of referencing things or adding eventlisteners via old sytle javascript. This i think determs alot of people, they do have a community support forums but that can also at times be discouraging, as it may take a couple of bumps to get a question answered.
In my opinion the Ext documentation could take a lesson from the PHP documentation and add common examples in this notation style format, for the various things you may want to do with an object/widget/datastore.
In the end Ext is a great product with a bright future and just needs to polish its documentation as well as it has its interface objects.
