The document discusses Flickr APIs and how they can be used to build applications. It describes PhotoSoup, an app that uses Flickr photos as hints in a word search puzzle, pulling relevant photos through the Flickr search API. Another app called TagExplorer is shown, which allows users to explore photos based on tags. The document encourages hacking with Flickr APIs and provides example API calls and links to documentation on building apps with the Flickr platform.