Done

application.rb

@@ -2,7 +2,7 @@ class Application
 
   def call(env)
     resp = Rack::Response.new
-    resp.write "Hello, World"
+    resp.write "Hello, my name is"
     resp.finish
   end
 

first.ru

@@ -0,0 +1,9 @@
+require 'rack'
+
+# Instances of Proc automatically have a call method that runs the block that
+# they're initialized with.
+my_server = Proc.new do
+  [200, { 'Content-Type' => 'text/html' }, ['<em>Hello</em>']]
+end
+
+run my_server

second.ru

@@ -0,0 +1,14 @@
+require 'rack'
+
+# Something that responds to call, that's what Rack demands
+class MyServer
+    def call(env)
+      return [ 200, {'Content-Type' => 'text/html'}, "Hello, my name is" ]
+    end
+
+    def pretty_response
+      (Time.now.to_i % 2).zero? ?  ["<em>Hello</em>"] : ["<strong>Hello</strong>"]
+    end
+end
+
+run MyServer.new

third.ru

@@ -0,0 +1,2 @@
+require_relative './my_server'
+run MyServer.new