Hold on Tight bookshelf. A brightly-coloured aluminum cube and oversized wing nut serve as a sliding bookend which can be adjusted and secured wherever it is needed, whether your book collection is growing or shrinking.
ooh this is great for unfinished basement stairs (book-staircase). I love the idea of book shelves in between the stairs. This would be especially helpful for a small home and a book lover that needed more shelves.