I couldn’t find the price or license on the web site. Is this free? How much does it cost?
yEd is freeware. You can see the license by clicking one of the download links. I guess they monetize it by licensing the underlying diagramming libraries to businesses from the looks of it.
DbVisualizer licenses one of their libraries for its ERD feature: https://www.dbvis.com/images/features/screens/navigator1.png