The core functionality is based on FBReader
source code with a few modifications. Books are imported from the Downloads folder,
where they are saved by the browser or email client. Alternatively, you can
manually copy your books to the Documents/Books directory under the home
folder. Removable storage is supported as well, the books are stored in the
/Books directory there.
In theory, it should be able to handle all E-book formats supported by FBReader. Tested mostly with epub and fb2.