This is Broken - A tribute to Seth Godin's book recommendations
Liist.cc - A tool that turns your photos, notes, and maps into shareable recommendations - fully automated.
Booknshelf - Social book and bookshelf discovery platform.
Likewise - Get recommendations you love, from people you know.
Kooba - An interactive graph for finding new books
Alternative To by SaaSHub - Find the alternative to every product with a single click