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 [1]...
And when they say "simplifying", they mean "simplifying"!
If you need some convincing, check out this video (11m20s):
AribaWeb: Rich Widgets and AJAX Integration [2] from AribaWeb Team [3] on Vimeo [4].
Links:
[1] http://sourceforge.net/project/showfiles.php?group_id=227584&package_id=275548
[2] http://vimeo.com/1827249
[3] http://vimeo.com/user767463
[4] http://vimeo.com