www.oreilly.com -- O'Reilly Open Books Project
Over the years, O'Reilly Media has published a number of "Open Books"--books with various forms of "open" copyright. The reasons for "opening" copyright, as well as the specific license agreements under which they are opened, are as varied as our authors.
O'Reilly の Open Books では、フリーでダウンロードできる書籍が一覧で見れます。野良ですが RSS もアリ。