Goodreads - See what your friends are reading.
100 Million Books - Discover books every time you open a new Chrome tab.
LibraryThing - A home for your books.
Bookshop UK - Support local bookshops
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes
Booknshelf - Social book and bookshelf discovery platform.