While searching the database for your required books by author, title or subject.
Ebrary offers an increasing selection of more than 20,000 e-books in business, economics, computers, engineering, and technology.
Free Online Books: Listing more than 35,000 English works in various formats.
Textbooks in the Open Textbook Library are considered open because they are free to use and distribute, and are licensed to be freely adapted or changed with proper attribution.
OAPEN promotes and supports the transition to open access for academic books by providing open infrastructure services to stakeholders in scholarly communication.
The Internet Archive is building a digital library of Internet sites and other cultural artefacts in digital form. Like a paper library, it provides free access to researchers, historians, scholars, people with print disabilities, and the general public.
While searching database for your required books by author, title or subject, use keywords i.e.Math, Calculus, Geography, Electrical Engineering,Physics, Calculus etc.