what is the kindle format extension?
<answer> Calibre is a free, open-source e-book manager that lets users convert EPUB files to Kindle-readable MOBI files. <context> If you use an e-reader, it's probably a Kindle, which means it can be a pain to use open-source e-book formats like EPUB. Calibre is a free, open-source e-book manager that lets users convert EPUB files to Kindle-readable MOBI files. Here's how to use it: Download and install Calibre.