diff --git a/middleman-core/lib/middleman-core/configuration.rb b/middleman-core/lib/middleman-core/configuration.rb
index 7d8fc8db..b75c2e8e 100644
--- a/middleman-core/lib/middleman-core/configuration.rb
+++ b/middleman-core/lib/middleman-core/configuration.rb
@@ -165,16 +165,12 @@ module Middleman
       # mode and no new settings may be defined.
       def finalize!
         @finalized = true
+        self
       end
 
       # Deep duplicate of the configuration manager
       def dup
-        copy = ConfigurationManager.new
-        @settings.each do |key, setting|
-          copy_setting = copy.define_setting(setting.key, setting.default, setting.description)
-          copy_setting.value = setting.value if setting.value_set?
-        end
-        copy
+        ConfigurationManager.new.tap {|c| c.load_settings(self.all_settings) }
       end
 
       # Load in a list of settings
diff --git a/middleman-core/lib/middleman-core/core_extensions/extensions.rb b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
index 44d4b7d1..7515a631 100644
--- a/middleman-core/lib/middleman-core/core_extensions/extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
@@ -62,22 +62,12 @@ module Middleman
           send("#{env}_config", &block)
         end
 
-        # Alias `extensions` to access registered extensions
-        #
-        # @return [Array<Module>]
-        def extensions
-          @extensions ||= []
-        end
-
         # Register a new extension
         #
         # @param [Module] extension Extension modules to register
         # @param [Hash] options Per-extension options hash
         # @return [void]
         def register(extension, options={}, &block)
-          @extensions ||= []
-          @extensions += [extension]
-
           if extension.instance_of? Module
             extend extension
             if extension.respond_to?(:registered)
@@ -87,6 +77,7 @@ module Middleman
                 extension.registered(self, options, &block)
               end
             end
+            extension
           elsif extension.instance_of?(Class) && extension.ancestors.include?(::Middleman::Extension)
             extension.new(self, options, &block)
           end
@@ -107,17 +98,24 @@ module Middleman
           ext_module = if ext.is_a?(Module)
             ext
           else
-            ::Middleman::Extensions.load(ext.to_sym)
+            ::Middleman::Extensions.load(ext)
           end
 
           if ext_module.nil?
             logger.error "== Unknown Extension: #{ext}"
           else
             logger.debug "== Activating: #{ext}"
-            self.class.register(ext_module, options, &block)
+            extensions[ext] = self.class.register(ext_module, options, &block)
           end
         end
 
+        # Access activated extensions
+        #
+        # @return [Hash<Symbol,Middleman::Extension|Module>]
+        def extensions
+          @extensions ||= {}
+        end
+
         # Load features before starting server
         def initialize
           super
@@ -149,7 +147,7 @@ module Middleman
           run_hook :after_configuration
 
           logger.debug "Loaded extensions:"
-          self.class.extensions.each do |ext|
+          self.extensions.each do |ext,_|
             logger.debug "== Extension: #{ext}"
           end
         end
diff --git a/middleman-core/lib/middleman-core/core_extensions/request.rb b/middleman-core/lib/middleman-core/core_extensions/request.rb
index 99f6a9be..af42008b 100644
--- a/middleman-core/lib/middleman-core/core_extensions/request.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/request.rb
@@ -37,15 +37,7 @@ module Middleman
         #
         # @private
         def reset!
-          @app = nil
-        end
-
-        # The shared Rack instance being build
-        #
-        # @private
-        # @return [Rack::Builder]
-        def app
-          @app ||= ::Rack::Builder.new
+          @rack_app = nil
         end
 
         # Get the static instance
@@ -74,21 +66,23 @@ module Middleman
         # @private
         # @return [Rack::Builder]
         def to_rack_app(&block)
-          inner_app = inst(&block)
+          @rack_app ||= begin
+            app = ::Rack::Builder.new
+            app.use Rack::Lint
 
-          app.use Rack::Lint
+            Array(@middleware).each do |klass, options, blockm|
+              app.use(klass, *options, &block)
+            end
 
-          (@middleware || []).each do |m|
-            app.use(m[0], *m[1], &m[2])
+            inner_app = inst(&block)
+            app.map("/") { run inner_app }
+
+            Array(@mappings).each do |path, block|
+              app.map(path, &block)
+            end
+
+            app
           end
-
-          app.map("/") { run inner_app }
-
-          (@mappings || []).each do |m|
-            app.map(m[0], &m[1])
-          end
-
-          app
         end
 
         # Prototype app. Used in config.ru
diff --git a/middleman-core/lib/middleman-core/extensions.rb b/middleman-core/lib/middleman-core/extensions.rb
index 64df512b..6000877a 100644
--- a/middleman-core/lib/middleman-core/extensions.rb
+++ b/middleman-core/lib/middleman-core/extensions.rb
@@ -114,15 +114,15 @@ module Middleman
 
     attr_accessor :app, :options
 
-    def initialize(klass, options_hash={}, &block)
-      @options = ::Middleman::Configuration::ConfigurationManager.new
-      @options.load_settings(self.class.config.all_settings)
+    def initialize(klass, options_hash={})
+      @options = self.class.config.dup
+      @options.finalize!
 
       options_hash.each do |k, v|
         @options[k] = v
       end
 
-      block.call(@options) if block_given?
+      yield @options if block_given?
 
       ext = self
       klass.after_configuration do
@@ -132,7 +132,6 @@ module Middleman
     end
 
     def after_configuration
-
       nil
     end
   end
diff --git a/middleman-core/lib/middleman-core/meta_pages.rb b/middleman-core/lib/middleman-core/meta_pages.rb
index 042ef89d..1c0eec4c 100644
--- a/middleman-core/lib/middleman-core/meta_pages.rb
+++ b/middleman-core/lib/middleman-core/meta_pages.rb
@@ -45,7 +45,7 @@ module Middleman
 
       # Inspect the sitemap
       def sitemap(env)
-        resources = @middleman.sitemap.resources(true)
+        resources = @middleman.inst.sitemap.resources(true)
 
         sitemap_tree = SitemapTree.new
 
@@ -58,7 +58,8 @@ module Middleman
 
       # Inspect configuration
       def config(env)
-        template('config.html.erb', :config => @middleman.config)
+
+        template('config.html.erb', :config => @middleman.inst.config, :extensions => @middleman.inst.extensions, :registered_extensions => Middleman::Extensions.registered.dup)
       end
 
       private
diff --git a/middleman-core/lib/middleman-core/meta_pages/templates/config.html.erb b/middleman-core/lib/middleman-core/meta_pages/templates/config.html.erb
index c7b3d6b7..f043ec07 100644
--- a/middleman-core/lib/middleman-core/meta_pages/templates/config.html.erb
+++ b/middleman-core/lib/middleman-core/meta_pages/templates/config.html.erb
@@ -2,18 +2,19 @@
 <html>
   <head>
     <meta charset="utf-8">
-        
+
     <title>Middleman Config</title>
   </head>
-  
+
   <body>
     <h1>Middleman Config</h1>
     <a href="../">More meta pages</a>
 
+    <h2>Core Configuration</h2>
     <ul>
     <% config.all_settings.each do |setting| %>
       <li>
-        <b><%= setting.key %></b>: 
+        <b><%= setting.key.inspect %></b>:
         <%= setting.value.inspect %>
         <% if setting.value_set? %>
           <br>
@@ -26,6 +27,44 @@
       </li>
     <% end %>
     </ul>
+
+    <h2>Extensions</h2>
+    <ul>
+      <% extensions.each do |ext_name, extension| %>
+      <li>
+        <% registered_extensions.delete(ext_name) %>
+        
+        <b><%= ext_name.inspect %></b> (Active)
+        <% if extension.is_a?(::Middleman::Extension) && !extension.options.all_settings.empty? %>
+        <br>
+        <b>Options:</b>
+        <br>
+        <ul>
+          <% extension.options.all_settings.each do |setting| %>
+          <li>
+            <b><%= setting.key.inspect %></b>:
+            <%= setting.value.inspect %>
+            <% if setting.value_set? %>
+            <br>
+            Default: <%= setting.default.inspect %>
+            <% else %>
+            (Default)
+            <% end %>
+            <br>
+            <i><%= setting.description %></i>
+          </li>
+          <% end %>
+        </ul>
+        <% end %>
+      </li>
+
+      <% end %>
+
+      <% registered_extensions.keys.each do |ext_name| %>
+      <li><b><%= ext_name.inspect %></b> (Inactive)</li>
+      <% end %>
+    </ul>
+
   </body>
 </html>
 
diff --git a/middleman-core/lib/middleman-core/preview_server.rb b/middleman-core/lib/middleman-core/preview_server.rb
index fa35983d..7296712c 100644
--- a/middleman-core/lib/middleman-core/preview_server.rb
+++ b/middleman-core/lib/middleman-core/preview_server.rb
@@ -19,6 +19,7 @@ module Middleman
 
         mount_instance
         logger.info "== The Middleman is standing watch at http://#{host}:#{port}"
+        logger.info "== Inspect your site configuration at http://#{host}:#{port}/__middleman/"
 
         @initialized ||= false
         unless @initialized
@@ -77,7 +78,15 @@ module Middleman
     private
       def new_app
         opts = @options
-        @app =::Middleman::Application.server.inst do
+        server = ::Middleman::Application.server
+
+        # Add in the meta pages application
+        meta_app = Middleman::MetaPages::Application.new(server)
+        server.map '/__middleman' do
+          run meta_app
+        end
+
+        @app = server.inst do
           if opts[:environment]
             config[:environment] = opts[:environment].to_sym
           end
@@ -166,13 +175,6 @@ module Middleman
         start_file_watcher
 
         rack_app = app.class.to_rack_app
-
-        # Add in the meta pages application
-        meta_app = Middleman::MetaPages::Application.new(app.class.inst)
-        rack_app.map '/__middleman' do
-          run meta_app
-        end
-
         @webrick.mount "/", ::Rack::Handler::WEBrick, rack_app
       end
 
diff --git a/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb b/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
index 1eb1796c..c2aa42dc 100644
--- a/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
+++ b/middleman-core/lib/middleman-core/templates/extension/lib/lib.rb
@@ -2,42 +2,39 @@
 require "middleman-core"
 
 # Extension namespace
-module MyExtension
-  class << self
+module MyExtension < Middleman::Extension
+  option :my_option, "default", "An example option"
 
-    # Called when user `activate`s your extension
-    def registered(app, options={})
-      # Include class methods
-      # app.extend ClassMethods
+  def initialize(app, options_hash={})
+    # Call super to build options from the options_hash
+    super
 
-      # Include instance methods
-      # app.send :include, InstanceMethods
+    # Require libraries only when activated
+    # require 'necessary/library'
 
-      app.after_configuration do
-        # Do something
-      end
-    end
-    alias :included :registered
+    # Include helpers or instance methods for the Middleman app
+    # app.send :include, Helpers
+
+    # set up your extension
+    # puts options.my_option
   end
 
-  # module ClassMethods
-  #   def a_class_method
-  #   end
-  # end
+  def after_configuration
+    # Do something
+  end
 
-  # module InstanceMethods
-  #   def an_instance_method
+  # module Helpers
+  #   def a_helper
   #   end
   # end
 
 end
 
-
 # Register extensions which can be activated
 # Make sure we have the version of Middleman we expect
 # ::Middleman::Extensions.register(:extension_name) do
 #
-#   # Return the extension module
+#   # Return the extension class
 #   ::MyExtension
 #
 # end
diff --git a/middleman-more/lib/middleman-more.rb b/middleman-more/lib/middleman-more.rb
index df73efa9..c4c771fe 100644
--- a/middleman-more/lib/middleman-more.rb
+++ b/middleman-more/lib/middleman-more.rb
@@ -83,7 +83,7 @@ module Middleman
         # to avoid browser caches failing to update to your new content.
         Middleman::Extensions.register(:asset_hash) do
           require "middleman-more/extensions/asset_hash"
-          Middleman::Extensions::AssetHash
+          Middleman::Extensions::AssetHash::Extension
         end
 
         # AssetHost allows you to setup multiple domains to host your static
diff --git a/middleman-more/lib/middleman-more/extensions/asset_hash.rb b/middleman-more/lib/middleman-more/extensions/asset_hash.rb
index 2390e1f4..ca710a4b 100644
--- a/middleman-more/lib/middleman-more/extensions/asset_hash.rb
+++ b/middleman-more/lib/middleman-more/extensions/asset_hash.rb
@@ -1,27 +1,29 @@
 module Middleman
   module Extensions
     module AssetHash
-      class << self
-        def registered(app, options={})
+      class Extension < ::Middleman::Extension
+        option :exts, %w(.jpg .jpeg .png .gif .js .css .otf .woff .eot .ttf .svg), "List of extensions that get asset hashes appended to them."
+        option :ignore, [], "Regexes of filenames to skip adding asset hashes to"
+
+        def initialize(app, options_hash={})
+          super
+
           require 'digest/sha1'
           require 'rack/test'
           require 'uri'
-
-          exts = options[:exts] || %w(.jpg .jpeg .png .gif .js .css .otf .woff .eot .ttf .svg)
-
-          # Allow specifying regexes to ignore, plus always ignore apple touch icons
-          ignore = Array(options[:ignore]) << /^apple-touch-icon/
-
-          app.ready do
-            sitemap.register_resource_list_manipulator(
-              :asset_hash,
-              AssetHashManager.new(self, exts, ignore)
-            )
-
-            use Middleware, :exts => exts, :middleman_app => self, :ignore => ignore
-          end
         end
-        alias :included :registered
+
+        def after_configuration
+          # Allow specifying regexes to ignore, plus always ignore apple touch icons
+          ignore = Array(options.ignore) + [/^apple-touch-icon/]
+
+          app.sitemap.register_resource_list_manipulator(
+            :asset_hash,
+            AssetHashManager.new(app, options.exts, ignore)
+          )
+
+          app.use Middleware, :exts => options.exts, :middleman_app => app, :ignore => ignore
+        end
       end
 
       # Central class for managing asset_hash extension
@@ -38,6 +40,7 @@ module Middleman
           # Process resources in order: binary images and fonts, then SVG, then JS/CSS.
           # This is so by the time we get around to the text files (which may reference
           # images and fonts) the static assets' hashes are already calculated.
+          rack_client = ::Rack::Test::Session.new(@app.class.to_rack_app)
           resources.sort_by do |a|
             if %w(.svg).include? a.ext
               0
@@ -51,7 +54,6 @@ module Middleman
             next if @ignore.any? { |ignore| Middleman::Util.path_match(ignore, resource.destination_path) }
 
             # Render through the Rack interface so middleware and mounted apps get a shot
-            rack_client = ::Rack::Test::Session.new(@app.class)
             response = rack_client.get(URI.escape(resource.destination_path), {}, { "bypass_asset_hash" => "true" })
             raise "#{resource.path} should be in the sitemap!" unless response.status == 200