Calibre is an all-in-one ebook management software that allows you to read, manage, and convert digital books. It supports a multitude of ebook file formats for both reading and conversion purposes. It can sync your book collection and reading progress across multiple devices. Calibre is a completely free and open-source app, being in development for over a decade. It is considered to be one of the most feature-packed and comprehensive ebook management suites available for desktop PCs.
Foliate is a free and open-source ebook reader for Linux. It aims to provide a clean, modern, and distraction-free interface for reading books on desktop computers. Its feature set is on par with other popular ebook readers and includes all necessary options for changing the book styles and formatting, syncing the reading progress, user bookmarks, text search, dictionary lookup, and so on. Foliate also comes with basic text-to-speech support for ebooks, something that other desktop readers lack.