WebTAP is a public interest and research project at Princeton University looking into how Web entities track users through a variety of techniques. Based upon rigorous research methods they provide the public at large with insights and policy recommendations regarding online privacy.
OpenWPM is the software framework that WebTAP uses to conduct a large scale census of websites:
OpenWPM is a web privacy measurement framework which makes it easy to collect data for privacy studies on a scale of thousands to millions of site. OpenWPM is built on top of Firefox, with automation provided by Selenium. It includes several hooks for data collection, including a proxy, a Firefox extension, and access to Flash cookies. Check out the instrumentation section below for more details.
OpenWPM is the basis of an extensive academic publication (which I need to read).
The cherry on top is collection documentation and archiving of their Web census data. According to a recent blog post on a new notebook wrapper around the Web Census data, they collect 500GB of data on a monthly basis. Juicy!
Great work by computer science and policy researchers on behalf of the greater good.