I’m not getting this yet, but looks like visualisation + something else… the visuals look good though (but requiring an awful lot of JS), so worth investigating some time later, this is what the site says:
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’s emphasis on web standards gives you the full capabilities of modern browsers without tying yourself to a proprietary framework, combining powerful visualization components and a data-driven approach to DOM manipulation.