This is an experimental navigation menu by Bennett Feely. When you click on the menu button on the top right it expands into a series of concentric circles to display the navigation menu, you can click on it again to collapse the menu.
If you are having trouble with the pen, try the archived copy on GitHub
Rings Navigation Menu Snippet
See the Pen Rings Navigation Concept by Bennett Feely (@bennettfeely) on CodePen.0