AribaWeb - The platform to simplify your development...

AribaWeb is the Open Source component-based web application development framework for creating rich, AJAX-enabled applications with the absolute minimum of code (and no hand-coded Javascript).

Currently, version 5 is RC1 and is available here...

And when they say "simplifying", they mean "simplifying"!
If you need some convincing, check out this video (11m20s):

AribaWeb: Rich Widgets and AJAX Integration from AribaWeb Team on Vimeo.