After seeing @Gregozor2121 share, I searched around in my bookmarks for similar stuff. Here are a couple of links that I feel is useful for everyone:

A massive list of Free programming books.
https://ebookfoundation.github.io/f...
(Also do explore anything marked as "awesome", cause it literally is awesome!! They have got tons of lists of resources for most programming languages, free software lists, famous stackoverflow answers, quotes & even Pokemon!!)

I also had this bookmarked:
https://github.com/chubin/cheat.sh
Basically cheat sheets at your command line. Pretty neat utility.