I would prefer a good and free solution for reading
epub books on OS X.
It looks that by default OS X is not able to open epub books.
Stanza is a very good epub reader for OSX that is free.
Scarlett in the Mac App Store.
I use Calibre on my desktop machines; it's very feature rich and can convert to and from
.epub so you can use it with most of the "specialty" readers. You can even "tweak" your books to fix minor typos and oddities from conversions. I don't think that is up to the normal Mac usability, but it does work.
I've also used the Kobo reader to read various epubs; it has some nicer page layout than Calibre and allows comments and highlighting that is pretty unique to Kobo. I'll admit I haven't used it on Mac, but I think it's great on Windows and Android. I'm pretty sure it's Stanza on my iPad, though.
http://calibre-ebook.com/ might be a bit full featured but will do the job.
Bookle is a native epub viewer for OS X, but its development seems to have stopped at a kind of a beta stage. It doesn't support searching, and I didn't really like the full screen mode or the library model.
I have used calibre's ebook-convert to convert some epub files to plain text:
/Applications/calibre.app/Contents/MacOS/ebook-convert input.epub output.txt
E-Book Preview, http://macbookreader.com/wp/bookviewer (v.5.7 is the last full-featured free version) Bookreader Free, http://macbookreader.com/wp/ (there's also a paid version) Kitabu, www.kitabu.me Clearview, Canoe Software (App Store)
Stanza was freeware, copies are still lurking on the Internets.
Convert the EPUB into PDF for free. They email you the converted file in 2 minutes. Nothing to download, no trial, no partial download with a lure to buy the real deal.