SWAYAM

 https://swayam.gov.in/

Vidyamitra

 https://vidyamitra.inflibnet.ac.in/

MHRDs Virtual Labs

https://www.vlab.co.in/

NPTEL Courses

https://nptel.ac.in/

NDL of India

https://ndl.iitkgp.ac.in/

Shodhganga: A reservoir of Indian Theses

https://shodhganga.inflibnet.ac.in/

Wikibooks

https://en.wikibooks.org/wiki/Main_Page

Directory of Open Access Books (DOAB)  

https://doabooks.org/

Open Library

https://www.oapen.org/home

Project Gutenberg

https://www.gutenberg.org/

Rare Book Room

http://www.rarebookroom.org/

PDF Drive

https://www.pdfdrive.com/

N-LIST Database

https://nlist.inflibnet.ac.in/

NIScPR Online Periodicals Repository           

https://nopr.niscpr.res.in/

Directory of Open Access Journals

https://www.doaj.org/

Indian Academy of Science

https://insa.nic.in/ 

 Elsevier Journals

https://www.elsevier.com/en-in/open-access/open-access-journals

Science Direct – Free Open Access Journal

https://www.sciencedirect.com/

Springer Open Access

https://www.springeropen.com/journals

Hindawi Publishing

https://www.hindawi.com/journals/

Impact Journals          

http://www.impactjournals.us/index.php

National Library of Medicine

https://www.ncbi.nlm.nih.gov/

ABC-Chemistry: Directory of Free Full-Text Journals in Chemistry

https://abc-chemistry.org/

Wiley Browse Journals

https://authorservices.wiley.com/open-research/open-access/browse-journals.html

Taylor and Francis Online Open Journal

https://www.tandfonline.com/openaccess/openjournals

(MDPI) Multidisciplinary Digital Publishing Institute Open Access Journals

https://www.mdpi.com/about/journals

TOC -  provides access to tables of contents of over 11,155 scholarly journals

https://www.journaltocs.ac.uk/index.php?action=start

Google Scholar - Provides a search of scholarly literature

https://scholar.google.co.in/

OALIB is Open Access Library- More than 263,388 free accessible academic papers  are available  presently

https://www.oalib.com/

Encyclopedia.com      

https://www.encyclopedia.com/

Encyclopedia of Mathematics

https://encyclopediaofmath.org/wiki/Main_Page

New World Encyclopedia

https://www.newworldencyclopedia.org/

Wikipedia                   

https://en.wikipedia.org/wiki/Main_Page