NextApp's Echo2

Google has pretty much swept the AJAX field with its GWT - but a lot of fairly viable options remain on the table. Of these I've had a lot of experience with Echo2 from NextApp

Both Echo2 and GWT offer the advantage to developers of being able to develop purely in Java - a huge benefit to back end developers wanting to break out without necessarily having to kill themselves over browser anomalies and such.
However, they differ in a crucial way - GWT pushes practically all computing and state management to the client/browser. In effect they create a browser based/Javascript based JVM that runs the UI which is generated as a post compilation step from the Java code. This is great from a scalability perspective since the server just deals with data generation.
Echo2 on the other hand (soon to be Echo3) does on the fly rendering of the screen based on the Java code and does a lot of heavy lifting on the server including state management for all users.
The big benefit I felt from Echo2 was the fact that not only was everything pure Java at development time but it remained so at runtime as well. So debugging etc tended to be much smoother. Also the transparency of developing and running on the same JVM can be a pretty good thing for large volumes of code.

I have a fairly large application running off a Ubuntu+JBoss combination very stably for some time now and I believe it deserves at least one good look.

The differences between the 2 will continue to narrow with time so I will continue to update my opinions over the next few postings.