The National Digital library of India (NDLI) is a project under Ministry of Human Resource Development, India. The objective is to collect and collate metadata and provide full text index from several national and international digital libraries, as well as other relevant sources. It is a digital repository containing textbooks, articles, videos, audio books, lectures, simulations, fiction and all other kinds of learning media. The NDLI provides free of cost access to many books in English and the Indian languages.

Directory of Open Access Books is a joint service of OAPEN, OpenEdition, CNRS and Aix-Marseille Université......

PDF Drive is your search engine for PDF files. As of today we have 82,144,730 eBooks for you to download for free. No annoying ads, no download limits, enjoy it......

An open textbook is a textbook licensed under an open copyright license, and made available online to be freely used by students, teachers and members of the public. 

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. Thousands of volunteers digitized and diligently proofread the eBooks, for enjoyment and education.....

ManyBooks was established in 2004 with the vision to provide an extensive library of books in digital format for free on the Internet. Many of the early eBooks are from the Project Gutenberg archives, which means you will be able to find a lot of classics on the site.