Visual authoring of HTML5 user interfaces - in the browser!
Maqetta is an open source project that provides WYSIWYG visual authoring of HTML5 user interfaces. The Maqetta application itself is authored in HTML, and therefore runs in the browser without requiring additional plugins or downloads. Adress of site for this project: http://maqetta.org/
Maqetta is available under a commercial-friendly open source license. You can download the source code and install it on your own server, customize the code to fit your needs and/or contribute improvements to the open source project.