Data-Driven Documents (D3.js) is a data-driven library for DOM manipulation and a graphical toolkit with maximum compatibility, accessibility, and performance. It utilizes fully the capabilities of modern browsers and web standards (such as HTML, CSS, and SVG).
It is open source and hosted on GitHub (https://github.com/mbostock/d3) under a slightly modified BSD 3-clause license; therefore, it can be used in commercial products without being required to release any modifications. By the way, GitHub itself uses D3.js to visualize the contribution history of repositories.
Make yourself familiar with the wiki pages and the API reference on GitHub as they will become your companions during the next weeks: