Digging a bit further and reading about the author, I discovered GitBook. GitBook is an open source platform that let’s authors publish books for free using Markdown and Git. If you’re not familiar with these, don’t worry, you don’t need to know about this stuff just to read the books. There were 174 books to choose from when I last checked and many are offered in multiple languages.
Have a look and see if something catches your interest. I’m reading ProGit next.