Inside the folder mason/mason:

mvn clean install

The output should say:

[INFO] BUILD SUCCESS

1. Clone the project on your local machine, and import the Maven project.

File-> Import -> Existing Maven Projects -> Root Directory

2. Build and Install on the mason-build project.

Run as -> Maven install

To use MASON in 3D, you must install Java3D. Unfortunately, installing Java3D is not as easy as it once was. You can try Oracle's older distribution, but you may have more luck, particularly recent OS X version users, in installing Java3D and JOGL directly from the jogamp website. To do this, you'll need to install three Java3D libraries (j3dcore.jar, j3dutils.jar, and vecmath.jar), and a few JOGL libraries (gluegen-rt.jar gluegen-rt-natives-your-platform.jar, joal.jar, joal-all-natives-your-platform.jar, jogl-all.jar, and jogl-natives-your-platform.jar — look in a recent version directory like v2.1.4/jar; the jogamp-current/jar directory often has broken files).

Often the Java3D libraries are buggy and in flux for OS X users, so I've made a collection here for OS X which seems to work okay. Install these in your system-wide Java library location (on the Mac, it's /Library/Java/Extensions/). For more instructions, see this posting.