It's open-source (MIT), free and easy to use.
plotly.js ships with 20 chart types, including 3D charts, statistical graphs, and SVG maps.
Paper.js is an open source vector graphics scripting framework that runs on top of the HTML5 Canvas.
It offers a clean Scene Graph / Document Object Model and a lot of powerful functionality to create and work with vector graphics and bezier curves, all neatly wrapped up in a well designed, consistent and clean programming interface.
Chart.js is a simple, clean and engaging charts for designers and developers.
Tipue Search is a site search engine jQuery plugin. It's open source and responsive.
Tipue Search uses various modes for loading content. Static mode uses JSON, while Live mode grabs content from a list of pages. Tipue Image Search is a full image search plugin.
Leaflet is designed with simplicity, performance and usability in mind. It works efficiently across all major desktop and mobile platforms out of the box, taking advantage of HTML5 and CSS3 on modern browsers while still being accessible on older ones.
It can be extended with many plugins, has a easy to use and well-documented API and a simple, readable source code.
Mobify.js is an open source library for improving responsive sites by providing responsive images, JS/CSS optimization, Adaptive Templating and more.
Mobify.js also provides a “Capturing” API for manipulating the DOM before any resources have loaded, giving developers the ability to enable the listed features above without changing any backend markup.