Most books produced are either square or rectangular. For short run books, have you looked at custom shapes? The cheapest way to produce a custom shaped book is to design it so that the final trim is on a regular cutting machine.
The image above shows a 8.5” x 11” sheet of white paper inserted inside a custom shaped book. Note how the head (top) of the book is not at a right angle to the spine and the face of the book is cut on an angle.
For those books that can’t be trimmed that way, we can make casebound books that have an angled head or foot or face. For board books and perfect bound books, we can PMC high die cut books into custom shapes. For your next book job, make it a custom shape!