Calibre is an eBook manager that helps you organize your eBook collection, perform conversions between different eBook formats and synchronize the content of the program's database with that of some eBook reading devices.
As an eBook manager, Calibre lets you sort your eBook collection by title, author, date, publisher, rating, size, and series. It also supports tags and comments. The format conversion generates as output three types of documents: EPUB, LRF, and MOBI. The formats that Calibre accepts as input are MOBI, LIT, PRC, EPUB, ODT, FB2, HTML, CBR, CBZ, RTF, TXT, PDF and LRS.
Calibre can synchronize the information in its database with that of some eBook readers such as Sony PRS 500/505/700, Cybook Gen 3, Amazon Kindle (1 and 2), as well as the iPhone. Not only does it allow updating the metadata of eBooks stored in these devices, but you can also create collections from the tags defined in the program.
Other interesting features that Calibre offers is: transforming an RSS feed into an eBook, viewing eBooks using an integrated reader or remotely accessing Calibre's collection using a web browser.
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It is VERY convenient; it performs format conversion for Kindle on the fly and completes the metatags with the official book information.