free? GoLang books: Go in Action

It is not quite clear how this "free books" works, are those pre-final version or this is maybe done in collaboration with authors and publishers?

Free-Golang-Books/book at master · TechBookHunter/Free-Golang-Books @ GitHub

Free-Golang-Books/Go in Action.pdf at master · TechBookHunter/Free-Golang-Books @ GitHub

Go In Action | A book on the Go Programming Language

Manning | Go in Action

hint from podcast:
Go Systems with Erik St. Martin | Software Engineering Daily