If you want to jump straight to the moment when WP began its ascent to ubiquity, that moment is described here: https://github.com/WordPress/book/blob/master/Content/Part%2...

It's a neat book, and I like how it covers everything from the B2B fork to the ThemeForest GPL license fiasco.

That said, I do also kinda wish it'd started/finished a few years later, since the Rest API and Gutenberg would have made for interesting chapters. The former because of how it decoupled the front end from the dashboard, and the latter because of the various controversies surrounding it and how the quest for a new post editor ended up receiving a huge amount of backlash and even one full fork.

That would have made for an interesting ending. The book would describe WordPress beginning with a fork, and it'd end describing how Automattic's actions with Gutenberg may lead history to repeat once more.

So they wrote and published the book in Github? Is this a free service?