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O'Reilly provided examples of companies or products that embody these principles in his description of his four levels in the hierarchy of Web 2.0 sites:

Level-3 applications, the most "Web 2.0"-oriented, exist only on the Internet, deriving their effectiveness from the inter-human connections and from the network effects that Web 2.0 makes possible, and growing in effectiveness in proportion as people make more use of them. O'Reilly gave eBay, Craigslist, Wikipedia, del.icio.us, Skype, dodgeball, and AdSense as examples.
Level-2 applications can operate offline but gain advantages from going online. O'Reilly cited Flickr, which benefits from its shared photo-database and from its community-generated tag database.
Level-1 applications operate offline but gain features online. O'Reilly pointed to Writely (now Google Docs & Spreadsheets) and iTunes (because of its music-store portion).
Level-0 applications work as well offline as online. O'Reilly gave the examples of MapQuest, Yahoo! Local, and Google Maps (mapping-applications using contributions from users to advantage could rank as "level 2", like Google Earth). In addition, Gmail.

Characteristics

Flickr, A Web 2.0 web site that allows users to upload and share photosWeb 2.0 websites allow users to do more than just retrieve information. They can build on the interactive facilities of "Web 1.0" to provide "Network as platform" computing, allowing users to run software-applications entirely through a browser.[2] Users can own the data on a Web 2.0 site and exercise control over that data.[8][2] These sites may have an "Architecture of participation" that encourages users to add value to the application as they use it.[2][1] This stands in contrast to traditional websites, the sort that limited visitors to viewing and whose content only the site's owner could modify. Web 2.0 sites often feature a rich, user-friendly interface based on Ajax[2][1] and similar client-side interactivity frameworks, or full client-server application frameworks such as OpenLaszlo, Flex, and the ZK framework.[8][2].