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.

• New tool to set metadata in the actual book files in the calibre library from the updated metadata in the calibre database.
• calibredb: Add a new 'embed_metadata' command to update metadata in the actual book files in the calibre library from the calibre database.
• Edit Book: Allow customization of toolbars
• Add empty book: When adding empty book records to the library, add an option to also create empty EPUB files. Useful if you intend to subsequently edit these files with the calibre editor. You can access the add empty books feature by right clicking the Add Books button.
• Edit book: Remove unused CSS: Add an option to also remove unused class attributes from the HTML
• Edit book: Check Book: Add checks for empty HTML/XML/CSS/image files in the book.
• Edit Book: Check Book: Add checks for links whose fragment (the part after the #) points to a location that does not exist

• RTF metadata: Add proper support for unicode characters when reading and writing metadata to RTF files
• RTF metadata: Fix failure to write metadata to RTF files that do not already have an \info block
• Edit Book: Remove unused CSS: Handle @import rules when checking for unused CSS
• Edit Book: Remove unused css: Prevent failure when book has invalid items marked as stylesheets
• calibredb: Fix set_metadata not working for the series_index field.