Minstrel is the open source, MIT-licensed version of Menestrello, an hybrid app (currently, iOS and Android) for reading eBooks in several formats, including EPUB 2/3.
I introduced the project here:
https://www.mobileread.com/forums/sho...d.php?t=261762
Web page:
http://www.readbeyond.it/minstrel/index.html
GitHub:
https://github.com/readbeyond/minstrel/