This is a remake of a cantilevered bookshelf I made few years ago.  The concept is the same as the previous version, however I've simplified the design and eliminated any kind of connection pieces between the counter weight and the steel plate.  Essentially, this bookshelf can be made with one precast concrete counter weight, one structural steel channel, and one custom piece of sheet steel slotted down the middle to accomodate and adjustable bookend (not shown) to stop the books from toppling over as  they are placed farther down the shelf.