So another stumbling block that is fairly small I found while trying out Metasploit Unleashed was the install of The Dradis Framework.
The problem with OS X is some of the things, like Ruby, are a bit older. Not to mention the version shipped with OS X has some other problems. So I suggest taking the easy way and installing MacPorts. Once installed a few commands will have Ruby, Gems, and supporting plugins ready for you.
To get Ruby installed it is just:
sudo port install ruby
sudo port install rb-rubygems
To finish up everything you need for Dradis install the Gems as followed:
sudo gem install rails rake capistrano capistrano-ext libxml-ruby mongrel hpricot sqlite3-ruby
After all that is done you need to just reset and migrate the database. This can be done by going to the Dradis directory in shell and issuing the following:
rake db:migrate
rake dradis:reset
This should have everything you need to get Dradis up and going on OS X