Our goal for X3D is to make the native authoring and use of declarative XML-based X3D scenes natural and well supported for HTML5 authors, similar to the support provided for Scalable Vector Graphics (SVG) and Mathematical Markup Language (MathML).
Web3D Consortium's member Fraunhofer has developed X3DOM. More information on the X3dom project and example implementations are available at: www.x3dom.org.
Holger Seelig, an independent, has developed not only the Cobweb browser, but also the Titania X3D editor that runs on Ubuntu. More information on Cobweb, and many examples, are available at titania.create3000.de/cobweb.
This effort has strategic importance for Web3D and indeed for all 3D graphics, since X3D is an interchange format for a wide variety of models. We intend to establish a solid foundation for X3D to properly support 3D graphics in HTML5. Additional information on the X3D/HTML5 Web3D Working group and their current initiatives and efforts is available in our Wiki.