Web 2.0 is closely related to the idea of ‘Mashups‘: ‘
In technology, a mashup is a web application that combines data from more than one source into a single integrated tool; an example is the use of cartographic data from Google Maps to add location information to real-estate data from Craigslist, thereby creating a new and distinct web service that was not originally provided by either source.’ (from: Wikipedia.org)
The ProgrammableWeb Mashup Matrix (beta) lets you visualize the web mashup ecosystem.
This Matrix offers a quick way to see how many Mashups are composed (i.e. from which original Web2.0 websites)