Async JS and CSS
Converts render-blocking CSS and JS files into NON-render-blocking, improving performance of web page.
Plugin Tag: headjs
Asynchronous Javascript
Improve page load performance by asynchronously loading javascript using head.js
WP HeadJS
Uses HeadJS to load your enqueued scripts asynchronously, in parallel, executing them in order.
Head.WP
Head.js is a script to asynchronously load and manage dependencies of javascript and CSS assets.