In July 2016, Stack Overflow introduced Documentation Beta. Documentation is community-curated, example-focused developer documentation, based on the principles of Stack Overflow. In Stack Overflow Documentation, examples are the star of the show. Anyone can add one, so good topics will eventually have several useful examples. And much like answers on Stack Overflow, the most helpful ones will usually be voted up to be right on top.
In August 2017, the project was pulled out. Folks at Stack Overflow still think Documentation is a good idea. You can learn more about why this project was discontinued here.
There are many books that are compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA. Just because of the nature of the community curated work, the information presented in these books are not guaranteed to be correct nor accurate, use at your own risk. You can download the raw information of Stack Overflow Documentation Data Dump from here.