Ruby is the language leveraged in workflow nodes and connectors. These are some resources to help you better understand and use Ruby.
Programming Ruby - Book and website devoted to learning Ruby.
Programming Ruby: The Pragmatic Programmers' Guide, Second Edition is a fantastic book (ISBN 0974514055) dedicated to learning Ruby. It is a very good reference for experienced and unexperienced programmers alike. There is also a website, extracted from the first edition of the book, available here.
rubular.com - Web based regular expression editor and tester.
Regular expressions, also referred to as Regex and Regexp, provide a concise and flexible means to determine if a string of text matches a specific pattern. They are very commonly used to do a find and replace or to determine if an input string matches some set of requirements. Rubular.com provides a very easy to use interface for writing regular expressions and testing them against different strings of text.
JRuby Applet - Use JRuby code in your browser
This JRuby applet allow JRuby code to be executed in your browswer. Test JRuby/Ruby code in this applet before placing it in your tree. This can reduce testing cycles because the results of the code can be seen immediately
Ruby Documentation - Ruby Classes and Methods Documentation
Browse and search the Classes and Methods of Ruby. This documentation can be very useful when attempting understand what functionality is avaialable for use when writing Ruby code into your task tree. For example search the String Class to see how a String can be manipulated for node parameters.