CalibreBox opens multiple Calibre libraries from DropBox and OneDrive. It can sort, filter and search in these Calibre libraries to help you find any ebook and download it quickly.
It supports a host of different sort and filter options and can display all book metadata, including custom columns you set up in calibre.

Features:

Free:
• Up to 2 Calibre libraries
• Search in Titles, Tags, Authors and Comments
• Search suggestions and voice search
• Sort by Author, Title, Rating and several Date options - ascending and descending
• Filter by Dates, Rating and File Format
• Search shortcuts in detail view
• Zoom the book cover
• Visible marking of books that have been downloaded
• Show book list as regular list or cover grid
• Long-press actions for books in main list
• Share books via Dropbox links
• Several list layouts
• Support for Reading List plugin


Pro (In-App Purchase):
• Unlimited Calibre libraries
• Completely ad free
• Show custom columns in detail view
• Sort and Filter using custom columns
• Select a default format to use for downloads if available
• See the filsize of the default format or, if it is unavailable, the largest format in the detail view
• Filter for books that have already been downloaded
• Send to Kindle for compatible formats (requires Kindle app)
• Optional "swipe from book to book" feature in details
• Show book identifiers and link to source (like Amazon, Goodreads, etc)
• Option to list available formats and filesizes in details outside the download dialog

To add a Calibre library to Dropbox, open Calibre and select "Switch/create Library" from the menu, select an empty folder in your Dropbox folder, and choose the "Move current library to new location" option. Please wait until Dropbox has fully synchronised your Calibre library before attempting to open it in CalibreBox to avoid missing covers and failed book downloads.

The process works the same for OneDrive, just using the OneDrive folder on your computer.

Advanced users can also create a symlink or junction inside of the Dropbox folder pointing to the Calibre library folders.

For more information see http://hofferic.github.io/calibreboxpage/

Calibre is © Kovid Goyal - calibre-ebook.com
Dropbox is © Dropbox inc. - dropbox.com
OneDrive is © Microsoft - onedrive.com