X3D-Edit, by Don
Brutzman, et al, from the Naval
PostGraduate School in Monterey, California, is a tool for
editing, authoring, and validating X3D scenes. X3D-Edit is
written on top of the NetBeans Platform.
Here's a screenshot (click to enlarge it):
The related thesis can be found
here (PDF). It's very interesting to browse the X3D-Edit
site... for example, you find out about a number of interesting
plugins specifically made for this application, as well as other
generic...