Any section can be collapsible. In the Creative Child Theme we've implemented that as a great looking menu! We've added the Widget Section and just made it collapsible with a custom trigger! It's all responsive too!
“Element Bars, Widget Areas, Content/HTML/Shortcode sections, up to 4 variable width and visibility dependable layouts, useable on all pages/archives or single pages will just blow your mind away. Not ever seen in WP.”