There's no denying that Barnes & Noble's Nook business has faced challenges lately. The bookseller may, however, have an extra trick up its sleeve to keep e-reader buyers coming back. Taking a page from the likes of Apple and Amazon, it's expanding Nook Free Fridays to include apps in addition to books. The gesture effectively doubles the volume of free loot each week as long as you've got a tablet like a Nook HD or
