There are several brands--Docutech is one; Heidelberg is another.  These machines are able to print out a book in a ridiculously short period of time (a few minutes). Print a cover, bind it and voila, it's ready to go to the shipping department.  This is a far cry from traditional offset printing in which plates would have to be made of each page and then printed in large enough quantities to offset the price of the setup. Unlike offset printing, the digital setup is inexpensive, but the individual cost per book is more costly than offset.  The way it works out, it's generally cheaper to print on an offset press if you're going to print at least 1000 copies. If you're going to print fewer copies, it's cheaper to do the books on a digital press.