Calibre is a free and open-source e-book management software that allows users to manage their e-books, convert between different e-book formats, and sync e-books with various devices. It was first released in 2006 and has since become one of the most popular e-book management tools available.

One of the most notable features of Calibre is its ability to organize e-books into different categories and add tags, making it easy to search and locate specific books. It also allows users to edit the metadata of their e-books, including the title, author, and cover image, and can even download missing metadata from online sources.

Calibre also provides a powerful e-book conversion tool, allowing users to convert e-books from one format to another, such as from EPUB to MOBI, or from PDF to EPUB. This is particularly useful for those who want to read e-books on different devices that may not support the same file format.

In addition, Calibre supports a wide range of e-book readers, including Amazon Kindle, Barnes & Noble Nook, and Kobo e-readers, and can automatically sync e-books with these devices. It can also connect to online e-book stores, such as Amazon and Google Books, allowing users to browse and purchase e-books directly from within the software.

Calibre is an essential tool for anyone who reads and manages e-books. Its powerful features and easy-to-use interface make it a must-have for anyone looking to organize, convert, and sync their e-book library.

Key Features:

• Library management system to organize e-book collection
• Format conversion for compatibility with different devices
• Built-in editor to modify e-book metadata and table of contents
• E-book viewer with customization options
• Integrated web browser for downloading e-books
• Synchronization options for keeping e-book collection up-to-date across devices
• Extensible with plugins to add additional features and functionality.

• Edit book: Add a new tool to automatically arrange all files in the book into folders based on their type. Access it via Tools->Arrange into folders.
• Edit book: Add various validity checks for OPF files when running the Check Book tool.
• Check for incorrect idrefs, missing required sections, non-linear items in the spine, incorrect meta cover tags, duplicated items in the manifest or spine and so on.
• Edit book: Add checks for duplicate ids in HTML/OPF/NCX files
• Edit book: Add checks for filenames containing URL unsafe characters to the Check Book tool
• Conversion: Allow getting text for entries in the Table of Contents from tag attributes.

• AZW3 Output: When converting EPUB files that include an HTML titlepage and no external cover is specified, ensure that the Go to cover action on the Kindle goes to the cover image and not the HTML titlepage.
• Prevent setting an incorrect value for compression quality in the wireless driver causing an error
• Show a busy cursor while calibre is working on matching books on the device to books in the library, which can take a while if the user has a lot of books on the device.
• iTunes driver: Retry automatically a few times when failing to send multiple book to iTunes.
• HTML Input: Fix UTF-16/32 encoded files that are linked to from the parent file not being properly processed.
• EPUB Output: Fix splitting of large HTML files removing all child tags from inside

   tags.

• Edit book: Fix tab characters not being identified in the lower right corner.