the Beta Book Program of the Pragmatic Programmers:
A couple of months before a book is due to appear in its final form, we might release it under the Beta Book program. We’ll make two products available in our store:
* the Beta Book in PDF form
* the Beta Book/Paper book combo pack (PDF now, paperback when available)
Both items will be for sale at the regular price for these products (which means the combo pack will available for a substantial discount over buying the PDF and book separately).
The Beta Book only exists in PDF form. When you place your order for either of these products, we’ll ship you the Beta Book in its current state as a PDF.
When the final book is released, we’ll automatically ship you the final version of the PDF. If you ordered the combo pack, we’ll also ship you the physical book at this time.
and the Beta Chapters from upcoming books by O’Reilly – e.g. Skype Hacks