Ruby now come preinstalled on many Linux distributions, and Mac OS X includes Ruby). Try typing ruby -v at a command prompt--you may be pleasantly surprised.
If you don't already have Ruby on your system or if you'd like to upgrade to a newer version (remembering that this couse describes Ruby 1.9), you can install it pretty simply. What you do next depends on your operating system.
- Download http://railsinstaller.org/ from Apple Application Store :