D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG, and CSS. D3 emphasizes web standards and combines powerful visualization components with a data-driven approach to DOM manipulation, giving you the full capabilities of modern browsers without tying yourself to a proprietary framework.
Want to learn more? See the wiki.
For examples, see the gallery and mbostock’s bl.ocks.