From the webpage:
Vega is a visualization grammar, a declarative format for creating, saving and sharing visualization designs.
With Vega you can describe data visualizations in a JSON format, and generate interactive views using either HTML5 Canvas or SVG.
Read the tutorial, browse the documentation, join the discussion, and explore visualizations using the web-based Vega Editor.
vega.min.js (120K)
Of interest mostly because of its use with XDATA@Kitware for example.