FBReader is a free ebook reader. It support main ebook formats: ePub (including main features of ePub3), Kindle azw3 (mobipocket), fb2(.zip).
Other supported formats: RTF, doc (MS Word), html, plain text. FBReader is fast and highly customizable - it can use external TrueType/OpenType fonts and custom backgrounds, the screen brightness can be adjusted while reading (slide finger up/down along the left screen edge), and different day/night color schemes can be selected.
[Top ten] Good reading app
It's only flaw I can think of is the book adding interface - you have to load your collection one by one. Once they are on your Google account, this app offers an excellent UI that integrates with dictionaries and, with a plugin, also with TTS systems on your phone.
Tips for using the product
This app might not be as polished as the kindle app, but it is packed with more features... some of which I consider absolutely critical (like a sleep timer... so that when i fall asleep reading a book, i don't wake up in the morning with a dead battery).Perfect, nice, fast and simple Great day and night mode, useful system for annotations, fast access to table of contents.