Dojo Foundation provides Maqetta, a WYSIWYG HTML5 on-browser editor, that allows to design rich web applications layouts (also targets mobile devices). Is it based on HTML5, CSS3 and OpenAjax widgets metadata standard. It uses Dojo by default, and hooks are available to use another widgets library/toolkit (however they are not fully implemented yet, requiring modifying of Maqetta source code for now).
This editor is document-oriented (as defined in HTML), contrary to Atlas that creates Cappuccino-based applications (then relies on asbtraction layers, CoreGraphics and CoreAnimation implementations based on low level Canvas/VML browsers features).
We can also find Flux, a native(Cocoa) HTML5 editor, far more elegant (and that was priced very low for a few days at the Mac App Store). It doesn’t however feature widgets libbraries support, and only provides WebKit and jQuery animations support.
In both cases the bridge bewteen the client and server sides isn’t adressed (remote access for tables’s data, sort, master/detail views/CRUD cycle).