There are many other book makers. Problem is they assume you will use their own software or build the book in the web browser. If you build the book in Aperture and save the PDF file, you'll have trouble getting book printers to accept the file. (Caveat: my experience with this is several years old. I haven't tried lately)
One thing you can do is use the PDF menu in the Aperture Print dialog and choose to save each page you've designed as a separate TIFF or JPEG file. Then when you design the book with another book printer's SW (Blurb online for example), just choose full page layout for each page and use your Aperture exported pages to fill in each page of the new book.