world.rb

require 'pp'
require 'set'

def class_count
  puts ObjectSpace.each_object(Class){}
end

SKIPS = %w(debug gauntlet_rubygems monitor dl profile).map{ |l| "#{l}.rb" }

def require_all_the_things
  $LOAD_PATH.each do |dir|
    Dir[File.join(dir, '*.rb')].each do |path|
      lib = File.basename(path)
      next if SKIPS.include?(lib)

      begin
        require lib
      rescue LoadError
      end
    end
  end
end

class_count
require_all_the_things
class_count

world = Hash.new { |h,k| h[k] = Set.new }
ObjectSpace.each_object(Class) do |klass|
  world[klass.superclass] << klass
end

world.each { |k, v| world[k] = v.to_a }

pp world.to_a