I am not talking about books and encyclopaedias which are sold in bookstores are giving away for free. Wikipedia and Wikibooks are projects which contents are solely written by internet users or are adopted from public domain (free to use and distrubute). Wikipedia (http://www.wikipedia.org/) has enormous number of articles and increasing every day. Similar to the wikipedia project, wikibooks are also available for free and the books are well maintained therefore they are also very useful for internet users. The topics of the books is very broad including not only computer-related books but also books about language learning, and even recipes(!).