My iPad has iBooks which allows me to read EPUB format ebooks and PDFs. However, your lovely Mac cannot alone does not come with an EPUB reader. There are a few paid options in the Mac App Store but luckily I found 2 free non-App-Store options. I’m surprised there are not more decent open source options for reading EPUB files.
Although it’s massively bloated (224 MB) I have found Calibre to be a very good e-book reader. It’s interface is somewhat iTunes-like since it attempts to be a one-stop-shop for your EPUB needs. I don’t really like using library management interfaces like this and would like for a reader-only download.
[Update 6/15/2013] I’ve been told that Calibre can convert ebooks from one format to another. This is an interesting feature that I have not tried yet.
Stanza for Mac
Stanza was a great ebook reader for iOS/iPhone/iPad before iBooks or Kindle came out. Unfortunately Amazon bought Stanza and killed it. I haven’t even checked if Stanza is available in iTunes for iOS anymore. Nevertheless the spammy download sites like CNET and Brothersoft still have the last version of Stanza for Mac available for download. Stanza is a slimmer 35 MB download but its ebook rendering engine is not as good or accurate as Calibre.
At 92MB Azardi is much slimmer than Calibre and provides simple EPUB reading pleasure. The rendering is slightly more accurate than Stanza but wow the user interface on Azardi is comically difficult to wade through.
[Update 6/15/2013] – I’ve given Azardi a second look since it’s much smaller than the last time I looked at it. I have a small capacity Macbook Air so every MB counts on my HD! I can say that the rendering seems faithful to the EPUB and the application loads much faster than Calibre. The user interface to manage books is still a bit quirky to me but I don’t have a huge ebook library so it provides the straightforward EPUB-reading ability that I was looking for without a lot of bells and whistles.
List of EPUB reader software (Wikipedia)