Centless Books is described as 'CentslessBooks has thousands of bestselling free Kindle books, changing every day! We have thousands of free Kindle books in dozens of your favorite genres!' and is an website in the News & Books category. There are three alternatives to Centless Books, not only websites but also apps for SaaS and Windows. The best alternative is Project Gutenberg, which is free. Other great sites and apps similar to Centless Books are College Student Textbooks (Freemium) and PDFBooksWorld (Free).
Project Gutenberg is a library of over 60,000 free eBooks. Choose among free epub and Kindle eBooks, download them or read them online. You will find the world's great literature here, with focus on older works for which U.S. copyright has expired.