I like the concept of wikibooks. It is dynamic and it is collective. It can be modified and updated at any time - by me or by anybody else. A paper book is static and the publication process takes so long time that some of the information in the book may be outdated even before the book is published. My optimization manuals are also dynamic. Many people have asked me why I don't publish my manuals as books or journal articles, and people have offered to translate them to other languages. But that would spoil the idea of dynamic contents. I keep updating my manuals, and people send me corrections and additional information. Even the smallest error in my manuals is likely to be found by somebody who sends me an Email so that the error can be corrected in the next update. Paper books are not like that. They may contain obsolete information and errors that never get corrected. The concept of Wikibooks includes the necessary feature that you can track changes and undo changes. This makes the format a little clumsy, but that is a price I am willing to pay for a Web 2.0 concept. I have an idea that some day all of the resources on my website should go into a collective project, but I haven't found a suitable platform yet.