Hard-core book lovers and organizers, this is what you want. Up till now I've been using the Book Catalogue android app for my library of ~2000 books, which is great, but unfortunately has no syncable desktop or web version to go along with it. Though I generally prefer free (because I'm cheap) and open source (because I'm paranoid) software, I can definitely say that this is worth the money (for me, less than $5 a month). It seems like every other app or service of this kind is owned by amazon (LibraryThing, Goodreads), and not only is Collectorz free from their evil influence, they actually have a much better (not to mention better-looking) setup. There are more data fields than you can imagine, the display is highly customizable, and you can easily sync everything between the web and their android app. It has a good process for importing .csv files of your old book databases, and helps you match the old fields to the new ones so that the info doesn't get garbled in transition. Highly and enthusiastically recommended (and no, I'm not on their payroll! ;-).
Does not handle unlicensed Japanese manga very well.
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