This Thread contains generic material which is not specific to any programming language, but may be useful in any case.
As first Content I would love to signal the following telegram channel
This channel shows every book available for free on packtpub.org
This website has a huge range of free books for every technical topic, from database to language manuals
The most interesting part is the ‘free book of the day’ which is sent in that channel as message, with a link for an easy download
Have fun guys, stay awesome
Side Note: on request I can send the 1 GB Zip file with al the books I downloaded so far
Thanks for sharing.