BookReader is the Cocoa application for reading electronic books in the following formats:



calibre is described as 'Free e-book manager offering library management, multi-format conversion, syncing to devices, news download as e-books, built-in viewer, editor, and privacy' and is a leading Ebook Reader in the news & books category. There are more than 100 alternatives to calibre for a variety of platforms, including Windows, Android, Mac, Linux and Android Tablet apps. The best calibre alternative is KOReader, which is both free and Open Source. Other great apps like calibre are Librera Reader, Foliate, Koodo Reader and Readest.
BookReader is the Cocoa application for reading electronic books in the following formats:



Access for Students: With Raz-Kids, students can practice reading anytime, anywhere - at home, on the go, and even during the summer!




Raccoon Reader is a fast and simple reader for eBooks with large possibilities. The goal of authors is to create the best reader for Windows Phone 7, 8 and iOS.



The Kindle app puts millions of books, magazines, newspapers, comics, and manga at your fingertips.




Calibre is a book manager. It manages books collection and books metadata. It's like a librarian. Amazon Kindle is a book reader with a basic book management (it manages the titles of the books one bought) .
Amazon Kindle is a Kindle-only reading application



It is an e-book reader. It does mot manage libraries or convert formats.
The beta for Windows will be available in 2015. We're talking end 2018 now. Furthermore it is a reader only. Calibre is a book management system.
Calibre is about organization, library management, and conversion between different formats for just about any device. The fact that it happens to have a reader is almost inconsequential, thus recomending a piece of software that only reads is very unhelpful.

Aamazon kindle is far better than calibre, but for ebook management app (desktop), then amazon kindle is not an alternative.... not at all.