For those into ebooks—loading, transcoding, coding, or just reading—Calibre is nothing new to some. It is the only truly cross-platform application of its kind. No author producing (or researching) ebooks should be without it, and any reader should get to know it as well.
It is capable of transcoding purchased electronic texts into another format if you supply your login credentials for the vendor source. You will never again rely upon your purchaser account for a backup or the need to place your ebooks on any of your varied devices. And using a cloud service as a primary backup and delivery of ebooks is then no longer necessary.
There have been few but multiple instances of ebooks being redacted by a vendor and from the accounts of all purchasers. While refunds were given, that hardly compensates. And what if you change devices or have more than one of a different make / OS? You should not have to install a vendor’s app on every one of them.
It even has a way to author ebooks if you know how to export / save a word processor file to EPUB or XHTML Format. The internal ebook editor is good, though it does not match the power of Sigil. In addition, you have the legal right to make backup copies of any electronic product you purchase. So do so for your ebooks with Calibre.
NOTE: We had difficulty classifying this application, since it could be placed in multiple categories, including “Office” for reference texts. Since it is capable of transcoding and even authoring ebooks, and the maker of Sigil is involved as well, you can find links for Calibre under “Resources: Publishing.”