Disclosure: These instructions are provided as-is. I don't take any responsibility for things that might go wrong (though the worst thing that could happen should be that OCTGN just won't run). I don't have time to support you if things don't work, unfortunately. But hopefully you'll get OCTGN running without needing to use a virtual machine like Parallels or VirtualBox.
Statements like these are commands to be run in the terminal. You should be fine just copying and pasting, just don't miss any characters.
- Download OCTGN: http://octgn.net/Home/GetOctgn
- Launch Terminal.app
- Install Homebrew (a package manager for OS X)
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" - Install git
brew install git - If asked to install Command Line Tools, klick yes. Else
xcode-select --install - Install XQuarts
brew cask install xquartz