You must have Java 7 installed to compile it. I've switched to Java 7 because it's identical across all platforms now that the builds are provided directly by Oracle/Sun instead of Apple.
If you just want to try it out, download the pre-built version here:
avenue33:
I tried to compile and get the following error message:
-do-compile:
[javac] Compiling 21 source files to /Users/reivilo/Downloads/arduinox-master/build/classes
[javac] javac: invalid target release: 1.7
[javac] Usage: javac
[javac] use -help for a list of possible options
There was another nice project called Cocoduino (forum, GitHub).
Are you using the same approach based on ino (website, GitHub)?
You can even use Xcode, the excellent and free IDE provided with every Mac. Check the embedXcode project (website, download, forum!