What are some alternatives?
When comparing FBReader and Amazon Kindle, you can also consider the following products
calibre - Ebook manager, viewer & converter
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
The new iPad Pro - 10.5 inch - Thinner and better
Document Viewer - Document Viewer is a highly customizable document viewer for Android. - SufficientlySecure/document-viewer