ReConvert - Page builder to design thank you page that cross sell & upsell
Goodreads - See what your friends are reading.
In Cart Upsell - Boost revenue and increase average order size with the #1 upsell app for Shopify stores.
LibraryThing - A home for your books.
Shopify Upsell Bundles App - Shopify app to Create Bundles, Packages and Sets with discounts by the most simple and efficient...
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes