Keep multiple browsers & devices in sync when building websites. http://browsersync.io
Light and responsive lightbox plugin with focus on performance.
Micro check library
For slim progress bars like on YouTube, Medium, etc
Full-sized drag & drop event calendar (jQuery plugin)
Automatically add a progress bar to your site. #hubspot-open-source
Parallax Engine that reacts to the orientation of a smart device
jQuery Mobile Framework
A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)
Delightful, performance-focused pure css loading animations.
UI automated testing framework based on node.js and selenium webdriver