Calibre is a free and open-source e-book management software that allows you to organize, convert, and read e-books in various formats on your computer or e-reader device. With Calibre, you can also sync your e-books to your devices and download news articles from the internet for reading later. It supports a wide range of e-book formats, including EPUB, MOBI, PDF, and many others. Additionally, Calibre comes with a built-in e-book reader, which allows you to read your e-books without needing a separate application.
Calibre server for iPhone/iPad
Calibre itself does not run on the iPhone/iPad, but you can connect to Calibre running on your Mac, read books and manage your library on the iDevice.
You can connect to Calibre using just Safari on your iPhone or iPad, and manage your collection and even read books in the browser, using the Calibre Content server.
A third-party companion app
There is an app called Calibre Companion that allows you to access your Calibre library on your iPhone or iPad.
This app is available for purchase on the App Store and it works by connecting to Calibre on your computer over Wi-Fi. Once you have set up the connection, you can browse and download your e-books from your Calibre library to your iPhone or iPad, and read them using the built-in e-book reader or any other compatible e-book reader app on your device.
Please note that the Calibre Companion app is not developed by the same team that develops Calibre, but it is designed to work with Calibre and provide an easy way to access your library on your mobile device.
Download
Download the free ebooks software from its official website below.