Dropzone is an easy to use drag'n'drop library. It supports image previews and shows nice progress bars.
A fast and fully-featured autocomplete library
React Native for Web
lightweight jquery date selector with multi-language support
An HTML5 saveAs() FileSaver implementation
HTTP mocking and expectations library
Prototype iPhone apps with simple HTML, CSS, and JS components.
motion graphics library for the web
Navigation scripting & testing utility for PhantomJS and SlimerJS
Parallax Engine that reacts to the orientation of a smart device
A positioning engine to make overlays, tooltips and dropdowns better #hubspot-open-source
HTML5 <audio> or <video> player with Flash and Silverlight shims that mimics the HTML5 MediaElement API, enabling a consistent UI in all browsers.