The instructions I use to add the extensions and libraries I favor (gems) using the RubyGems utility. (For instructions on installing the RubyGems utility, go here.)
Here are the gems I have installed. Use this script to replicate the installed extensions in future versions:
gem install rake # Build language gem install rspec # Behavior-Driven testing language gem install fxruby # GUI libarary (but keep an eye on WxRuby, see Which GUI?) gem install rails --include-dependencies # Web app language
To keep the libraries current, periodically issue this command:
gem update