Props to Woody for hand-holding and instructions on this.

There are 3 main ways to install Ushahidi 3.x on Mac OS:

• Using Vagrant virtual machine
• Using Homebrew to install mysql and run Ushahidi natively
• Use Mamp

Vagrant is generally recommended for Ushahidi 3.x because it allows you to isolate your environment, and you don't have to manage a *AMP (Apache-Mysql-Php) stack on your Mac.   Homebrew is recommended over Vagrant if you're going to develop other websites locally on your Mac. Mamp is last on the list of recommendations. 

External links:  Vagrant, Homebrew,  Mamp