I came across this free resource thought it will be useful for all of us who are looking to refer some material that we can have in our laptop or any other system. This is useful even if you don't internet connection where you are living currently. you just have to download the ebook material you need then use it later on when you don't have a active internet connection.
This below site lets you download pdfs without requiring any information to be given to them.That's what I like about this site, its simply awesome,I want to thank freecodecamps site from where I got this link.