Social Bookmarking, including: Stumbleupon, Bookmarksync, Delicious (website), Furl, Citeulike, Connotea, Givealink.org, Newsvine, Reddit, Google ... Popurls, Bibsonomy, Digg, Broowaha, Diigo

Hephaestus Books represents a new publishing paradigm, allowing disparate content sources to be curated into cohesive, relevant, and informative books. To date, this content has been curated from Wikipedia articles and images under Creative Commons licensing, although as Hephaestus Books continues to increase in scope and dimension, more licensed and public domain content is being added. We believe books such as this represent a new and exciting lexicon in the sharing of human knowledge. This particular book is a collaboration focused on Social bookmarking.

More info: Social bookmarking is a method for Internet users to organize, store, manage and search for bookmarks of resources online. Unlike file sharing, the resources themselves aren't shared, merely bookmarks that reference them.