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

keys 

        # Thread.keys

(from ruby core)
---
    thr.keys   -> array

---

Returns an array of the names of the fiber-local variables (as Symbols).

    thr = Thread.new do
      Thread.current[:cat] = 'meow'
      Thread.current["dog"] = 'woof'
    end
    thr.join   #=> #<Thread:0x401b3f10 dead>
    thr.keys   #=> [:dog, :cat]

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.