Ruby is already installed on OS X (at /usr/lib/ruby). Good starter sites are RubyGarden (follow the RubyNuby link for more info) & MacZealots. Main site

The default install may not be completely standard. There is a one-click install to create a parallel installation. Ruby can also be installed from source (good detailed instructions) (then located at /usr/local/src/ and /usr/local/bin/).

RubyGems is a package management system for Ruby (to easily add functions and features to the language). The manual and the installation instructions are available from the RubyGems site. (Packages are put at /usr/lib/ruby/gems/)

Using RubyGems:

Associated good things:

Installing: