This responsive Multi Level Dropdown Navigation Menu is built with Bootstrap 4.1 and available on Github.
Pushy is a Responsive Off Canvas jQuery Multilevel Navigation menu. Pushy is cross browser and even support the annoying Internet Explorer. Menu positions are adjustable.
stickup is a responsive jQuery plugin that can pin the navigation menu on top of the page. It is specifically designed for single page websites, but it can be re purpose for any type of website.
The multi toggle responsive navigation on smaller screens is similar to nested accordions, the user touches primary level parent item to reveal list under it and when the screen is big enough vertical toggle menu changes to horizontal drop down navigation.
If your website have hundreds of categories with each having their own sub categories and so on so forth. Then this Responsive CSS Mega Dropdown Menu is for you.