Great free plugin

Allows a huge number of settings, yet the frontend code is minimalistic. Uses the jQuery of WP for transitions / easing, so own JS is very small. The only problem is that it includes CSS styling directly in the head of each page, but you can first style the menu using the plugins great facilities, then copy the CSS to Custom CSS in WordPress or your theme, and finally select “No styling” in the accordeon widget. The absolutely best choice for performance freaks – improves your ranking on Google PageSpeed Insights! Knocks the stuffing out of bloated products with more users and reviews – small is beautiful.