This is a Ruby tree! It shows every object from the Ruby Programming Language in a tree format.

WeakRef::RefError

        # WeakRef::RefError < StandardError

(from ruby core)
---
RefError is raised when a referenced object has been recycled by the
garbage collector
---

      

This is MURDOC! A Ruby documentation browser inspired by Smalltalk-80. It allows you to learn about Ruby by browsing through its class hierarchies, and see any of its methods.