Vaadin Visual Editor is the name of the upcoming WYSIWYG editor for Vaadin applications. It will be part of the Vaadin Eclipse Plugin providing with nice round-trip code generation capabilities inside the IDE. However, as it is built with Vaadin, you can also run it as a stand-alone web application.
Here is a video introduction by Marc Englund:
The Visual Editor is still a work in progress and we are currently in version 0.8. Some features like the visual guidelines and grids have been implemented since this video was recorded. You can follow the live work in progress here: demo.vaadin.com/visualdesigner-nightly