Cx3D is a free, open-source and cross-platform application that is capable of simulating the growth of cortex in a 3D environment.
In other words, Cx3D can simulate the development of neural tissues: it enables cell division, migration, extension of neurites to form axonal and dendritic arbors, production, detection, synapses formation, and signaling molecules.
Being developed using Java, Cx3D is a cross-platform tool which can be used on any operating system that comes with Java support (e.g. Mac OS X, Windows, Linux).
Detailed instructions on how to install and use the Cx3D utility on your Mac are available HERE.