Oreilly And Associates have made many of their out-of-print books available at www.oreilly.com 
Among the books available are The Cathedral And The Bazaar by Eric Raymond; Free As In Freedom, a new biography of Richard Stallman; and Web Client Programming with Perl.
There are also books on Doc Book (Doc Book The Definitive Guide), Linux Os, and many of their out-of-print books.
See: Book List
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