And it has coins! 
Nah, seriously, over the time people read a wealth of books in the forums, and some of them are on the easier side actually. Some of the books are grouped into overarching book clubs, like the Beginner Book Club, but others are formed spontaneously by a group of interested people. You can get a good overview in the Master List of Book Clubs where the books are roughly labeled with a category.
The advantage of such a club is that usually there is a vocab sheet (at least for Beginner and often also for Intermediate) and people have already discussed the contents, asked questions and the like. And you can usually still ask questions there, as people often watch the threads even years after they finished the book.