Dropzone is an easy to use drag'n'drop library. It supports image previews and shows nice progress bars.
HTML5 <audio> or <video> player with Flash and Silverlight shims that mimics the HTML5 MediaElement API, enabling a consistent UI in all browsers.
Animate on scroll library
For slim progress bars like on YouTube, Medium, etc
lightweight jquery date selector with multi-language support
A simple, in-browser, markdown-driven slideshow tool.
MJML: the only framework that makes responsive-email easy
Keep multiple browsers & devices in sync when building websites. http://browsersync.io
A set of 170+ Bootstrap based design blocks ready to be used to create clean modern websites.
The 1kb client side MV* library
A lightweight library for manipulating and animating SVG
A jQuery typing animation script.