Using Mac OS X Mountain Lion, the installation of the zip RC3 did not work for me. I followed the instructions at
https://wiki.mobileread.com/wiki/Calibre2Opds_Installing for the Mac and copied every file from the zipped folder into my Java folder inside the COPDS package on my Mac. I then tried to change the rungui.sh using terminal, however, when I double-click on the rungui.sh now, it opens up in xcode, not as an executable shell. Also, when I open the "app" it shows up as version 3.1 rev 170.
Not sure where I screwed up...