This addon adds a Categories Menu dropdown to your store's Navigation Bar. This dropdown contains only the top level categories, so it will fit on all viewport sizes. This will work well for small stores that only have top-level categories, or in cases where the store owner does not care that subcategories are only listed on the category page.
If you have a store with subcategories and care about them being in the menu, this module is probably not for you.
NOTE: This software requires the Modular Navigation Bar Addon. Get that here: http://addons.oscommerce.com/info/9440
The support thread is here: http://forums.oscommerce.com/topic/409055-addon-modular-navigation-bar-bootstrap/