Keep your Calibre libraries on the iCloud and open them on your iPhone iPad and Mac or Windows pc.
Open your library anywhere on the world, search and open books. As many libraries as you like.
Open the books directly in the reader, no need for iTunes.
Stored querys. Create your own (complex) query. Autosuggest for the search. View the cover image and read the description. Search google for more information without leaving the app. Mark books for easy search in Calibre.
Everything is in the cloud, so all devices have the same information. And everything is availaballe in the whole world.