inventaire.io - Keep an inventory of your books. Share it with others. Discover the books available in your network!
Goodreads - See what your friends are reading.
LibraryThing - A home for your books.
BookLikes - BookLikes is a free blog platform for book lovers. 100% independent and free.
BookAuthority - BookAuthority collects the most recommended books on business, technology and science - as featured on CNN, Inc and Forbes
Riffle - Just good books and the readers who love them.