WP Fancy Menu plugin sets the menu and submenu that is displayed after the click. You can compress the whole block of the traditional menu into it and can place the menu anywhere you want on the edges of the browser.
You can also add multiple menus.
If you have too many menu items to display this is useful. Condense all the menu items into one button and when you click on the button, load all the menu items.
This is also useful if you have a minimalistic website and do not want to display a big menu bar.