The next Collaborative Web application that I'm not familiar with is Gapminder.
Gapminder provides access to searchable public data, however, the data is very visual and more easily understood because of Gapminder's philosophy. "Gapminder wants to make data more accessible and easier to use for instant visual analysis." Gapminder is providing tools so that people, independent of their political agenda, can freely "access the already existing statistics about global development to easily improve their understanding about the complex society" and how life has changed over time.
The site includes a tutorial that demonstrates how to use Gapminder's tools. There are video gapcasts and presentations, flash animations, and other resources which demonstrate how Gapminder tools make data come alive. Hans Rosling's lectures are awe inspiring. I especially liked his presentation, Debunking the myth of the "third world".
Public statistics which include a variety of indicators from life expectancy to internet use to military expenditures are available for most countries in the world. So teachers and students in many curricular areas could make use of this site.