CoolReader vs FBReader
CoolReader - an open-source program for reading electronic books in a variety of formats for Windows and Linux. There are also versions for OS Android and e-reading devices (LBook, PocketBook)
FBReader is an free eBook reader that supports numerous file formats like ePub, fb2, plucker, HTML, plain text, doc and more. You can also add multiple books at once in an archived format (tar, zip, gzip, bzip2). It supports embedded images, footnotes, hyperlinks, text search and full screen reading. It also has automatic bookmarking so that you don’t lose your place when closing a book.