One of the handiest features is the ability to download metadata about each book from online sources (Amazon, Barnes & Noble, Google, etc.). You can customize what information is shown about each book.

You can add tags(even custom tags) to each book to help you find them by category. I have about 150 e-books entered into the database and this program allows me to keep track of everything. So overall Calibre is definitely your one stop solution to all your e-book needs.

But most users would not know how to or bother to do it. If you are handy at changing themes, it can be done manually by changing the Resource/Image folder in the Programs folder. Various icons are used from different icon sets, so Calibre has no themed look to it. The worst thing that I can say about Calibre is that there should be a 'skin' or GUI option. There is no need to use another e-boook manager/reader unless your favorite e-book store forces you to use their own. Development support is constant with continuous updates frequently available. If a feature is not in Calibre, you can bet that it will be included sometime in the future. Anything that you could possibly want to do with your e-books can be done on Calibre, so there really is no reason to mention the functionality here. It is the most complete e-book manager/reader that I have used. You may find some good ones, but still not as good as Calibre. Try to find a better e-book manager/reader.

Calibre ebook review