When I finished reading Divergent, I wanted to know more about Four. I soon found out about Free Four. Free Four is Chapter 13 of Divergent told from Four's point of view. Then came along Allegiant with almost every other chapter from Four's point of view. That made my thirst for Four's point of view increase. Four: A Divergent Collection was my dream come true.
I haven't finished reading the whole series yet so, I haven't added a rating.
Here is the Goodreads link for Four: A Divergent Collection: http://www.goodreads.com/book/show/18126198-four