IBM announced a new tool for webdevelopers wanting to create interactive websites using HTML5.
It is called Maqetta and can be accessed here:

http://maqetta.org/

“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.”

Sounds promising!