<p>Protovis is a free, open source tool for composing custom views of data from simple elements such as bars or dots. Marks are defined through dynamic properties to allow inheritance, scales and layouts for simplified visualization construction. This tool uses JavaScript and SVG in order to ensure web-native visualizations. Protovis is no longer under active construction; many of the concepts used in its development have been implemented in its successor, D3.js.</p>