What open source program is the best example of Ruby programming to study to learn the language better?

Looking for a good open source program to study in order to pick up on the idioms of Ruby programming that make Ruby programs uniquely succinct, elegant, powerful, profound, and readable. I am looking for a program that when I study thee source code for it, it will show me the strengths of the language.

Sort of like design patterns but code patterns. You know, good idioms of the language that are in popular use.