Step 1: Inverted Bookshelf
The inverted bookshelf turns a bit of your living room upside down as it hangs all of the books from the bottom instead of supporting them from below. It's a satisfying optical trick and doesn't damage any of the books. In fact, you can take books in and out of it whenever you want.
Step 2: Materials
In addition to the basic materials for a shelf of wood and brackets, you will also need elastic webbing and a staple gun. The elastic that I'm using here can stretch beyond 200% of its original size and is certainly strong enough to hold the books here.
optional: glue gun
Step 3: Measure it out
The key things you need to figure out are how wide your books are and what length of elastic is good enough to support all of the books against the board without crushing them against it.
Measuring out my books, the average width was one inch and the ideal length of elastic turned out to be 14 inches.
Step 4: Staple the elastic to the board
Now that you have a length and a width, the next step is to staple gun two pieces of elastic down the middle of the board. I'm going to be suspending 12 books here, so I used just over 14 feet of material for each side.
Start each piece of elastic with the excess facing in. Staple this in place and fold the elastic back over to start running it down the board. Measure out 14 inches, staple it one inch farther and repeat until you get to the other end and fold the excess back inside again before stapling it.
Step 5: Insert books to test
I slid the books in and even the heaviest book was perfectly snug. It turned out that two straps was too much for the smaller books and started to compress them, so I only used the front strap and squished the other strap behind it.
Step 6: Add brackets and attach to wall
Now that you know that the shelf itself is stable, add a couple of brackets to the other side of the board. Then simply screw it into the wall.
Note: This was intended for a short term installation. To make it more permanent, I'd recommend hiding a couple L brackets on the underside.
Step 7: Sit back and enjoy
You can leave it as is or go for some more realism by gluing some toys, bookends, or even a fake drink to the bottom of the board to complete the look!