DDC or the Dewey Decimal Classification is a system that categorizes books according to subject matter. If you are looking for alternatives to DDC, there are other classification systems that you can consider. The Library of Congress Classification is a popular system used in academic institutions and government libraries. Another option is the Universal Decimal Classification which is widely used in Europe. Some librarians also use the BISAC or Book Industry Standards and Communications which is more popular in the United States. Regardless of the system you choose, the important thing is to organize your library in a way that makes it easy for patrons to find what they are looking for.