Protovis - A Graphical Toolkit for Data Visualization

Protovis composes custom views of data with simple marks such as bars and dots.
Unlike low-level graphics libraries that quickly become tedious for
visualization, Protovis defines marks through dynamic properties that encode
data, allowing inheritance, scales and layouts to simplify construction.

Protovis is free and open-source, provided under the BSD License. It uses
JavaScript and SVG for web-native visualizations; no plugin required (though you
will need a modern web browser)! Although programming experience is helpful,
Protovis is mostly declarative and designed to be learned by example.

This project is led by Mike Bostock and Jeff Heer of the Stanford Visualization
Group, with significant help from Vadim Ogievetsky. We welcome your
contributions and suggestions.

See also: https://github.com/mbostock/protovis