Librera is a free application for reading all book formats: PDF, EPUB, EPUB3, MOBI, DJVU, FB2, FB2.ZIP, TXT, RTF, AZW, AZW3, HTML, XPS, CBZ, CBR, TIFF and OPDS Catalgos with free books.
SpecsUpdate
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Pros
Pro Has all the functionality one needs - nothing is missing and there's nothing excessive
Best app so far.
Pro Fast animation
Pro FOSS
GPL v.3.
Pro Can read aloud texts
Customize the voice with pitch, speed and do whatever you want with it.
Pro UI and reading customization will blow your mind
You can even customize CSS code to fine-tune display of epub books. The best reader to handle online catalogs and TTS reading!
Cons
Con Free version contains ads
The Pro version has no problem. Alternatively, the fdroid version works as well, though it might be annoying to those who want cloud integration because the fdroid version doesn't have cloud integration.
Con No way to set a "home" folder
You have to press the back button a ridiculous amount of times to exit the app and then browse back to your books when you want to read again later.
Con Cannot reverse PDF reflow to return to normal view without exiting the PDF and opening again
Very annoying when you want to view graphics and tables etc.