Padraic Brady has made a post about the upcoming Zend Framework book (and website) he'll be releasing in January:

In January, the new book will commence its long awaited publishing process online. The book has been a long time coming since I started posting my now infamous tutorial series which focused on the practical side of creating an application more so than acting as a reference book. The book is being made available free of charge online funded by donations and some advertising.

The book will include the ability to comment on chapters (with changes to be included in possible revisions) via a jQuery-powered commenting system that allows for thoughts to be added to each paragraph. You can see the website in this screenshot.