swfobject : SWFObject 2 offers two optimized Flash Player embed methods; a markup based approach and a method that relies on JavaScript & offers a JavaScript API ...
howler.js : howler.js is an audio library for the modern web. It defaults to Web Audio API and falls back to HTML5 Audio.
Timeline : Beautifully crafted timelines that are easy, and intuitive to use.
impress.js : It's a presentation framework based on the power of CSS3 transforms and transitions in modern browsers and inspired by the idea behind prezi.com
Dropzone.js : DropzoneJS is an open source library that provides drag'n'drop file uploads with image previews.
Add Clippy or his friends to any website for instant nostalgia.