Main Page – Wikibooks
This looks as if it has some potential – as with other Wikis it’s an open content system that all can edit.
In this case, it’s a collection of books, with a vague “textbook” type emphasis. At the moment, it’s the cookbook that seems to be getting the most editing, though Programming in Ada is in at number 3, just ahead of Japanese.
Some of the books are a little thin on the ground, for example, the Usability book seems to have just have a definition & a table of proposed contents. Others, such as the Cell Biology one are more complete (though that was an electronic book already – on a lecturer’s website.)