diff --git a/.gitignore b/.gitignore
index 833a1503..2b4e408c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@ pkg
 Gemfile.lock
 docs
 .rbenv-*
+.ruby-version
 .*.swp
 build
 doc
@@ -15,4 +16,4 @@ doc
 tmp
 Makefile
 .mm-pid-*
-.idea
\ No newline at end of file
+.idea
diff --git a/middleman-core/lib/middleman-core/core_extensions/extensions.rb b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
index 7515a631..12469eed 100644
--- a/middleman-core/lib/middleman-core/core_extensions/extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
@@ -37,6 +37,7 @@ module Middleman
       class << self
         # @private
         def registered(app)
+          app.define_hook :initialized
           app.define_hook :after_configuration
           app.define_hook :before_configuration
           app.define_hook :build_config
@@ -68,19 +69,15 @@ module Middleman
         # @param [Hash] options Per-extension options hash
         # @return [void]
         def register(extension, options={}, &block)
-          if extension.instance_of? Module
-            extend extension
-            if extension.respond_to?(:registered)
-              if extension.method(:registered).arity === 1
-                extension.registered(self, &block)
-              else
-                extension.registered(self, options, &block)
-              end
+          extend extension
+          if extension.respond_to?(:registered)
+            if extension.method(:registered).arity === 1
+              extension.registered(self, &block)
+            else
+              extension.registered(self, options, &block)
             end
-            extension
-          elsif extension.instance_of?(Class) && extension.ancestors.include?(::Middleman::Extension)
-            extension.new(self, options, &block)
           end
+          extension
         end
       end
 
@@ -105,7 +102,22 @@ module Middleman
             logger.error "== Unknown Extension: #{ext}"
           else
             logger.debug "== Activating: #{ext}"
-            extensions[ext] = self.class.register(ext_module, options, &block)
+
+            if ext_module.instance_of? Module
+              extensions[ext] = self.class.register(ext_module, options, &block)
+            elsif ext_module.instance_of?(Class) && ext_module.ancestors.include?(::Middleman::Extension)
+              if ext_module.supports_multiple_instances?
+                extensions[ext] ||= {}
+                key = "instance_#{extensions[ext].keys.length}"
+                extensions[ext][key] = ext_module.new(self.class, options, &block)
+              else
+                if extensions[ext]
+                  logger.error "== #{ext} already activated. Overwriting."
+                end
+
+                extensions[ext] = ext_module.new(self.class, options, &block)
+              end
+            end
           end
         end
 
@@ -141,6 +153,8 @@ module Middleman
             instance_eval File.read(local_config), local_config, 1
           end
 
+          run_hook :initialized
+
           run_hook :build_config if build?
           run_hook :development_config if development?
 
@@ -148,7 +162,13 @@ module Middleman
 
           logger.debug "Loaded extensions:"
           self.extensions.each do |ext,_|
-            logger.debug "== Extension: #{ext}"
+            if ext.is_a?(Hash)
+              ext.each do |k,_|
+                logger.debug "== Extension: #{k}"
+              end
+            else
+              logger.debug "== Extension: #{ext}"
+            end
           end
         end
       end
diff --git a/middleman-core/lib/middleman-core/extensions.rb b/middleman-core/lib/middleman-core/extensions.rb
index 6000877a..b5fbc33d 100644
--- a/middleman-core/lib/middleman-core/extensions.rb
+++ b/middleman-core/lib/middleman-core/extensions.rb
@@ -1,3 +1,5 @@
+require "active_support/core_ext/class/attribute"
+
 module Middleman
 
   module Extensions
@@ -102,6 +104,8 @@ module Middleman
   end
 
   class Extension
+    class_attribute :supports_multiple_instances, :instance_reader => false, :instance_writer => false
+
     class << self
       def config
         @_config ||= ::Middleman::Configuration::ConfigurationManager.new
@@ -125,10 +129,11 @@ module Middleman
       yield @options if block_given?
 
       ext = self
-      klass.after_configuration do
+      klass.initialized do
         ext.app = self
-        ext.after_configuration
       end
+
+      klass.after_configuration(&method(:after_configuration))
     end
 
     def after_configuration
diff --git a/middleman-more/features/asset_host.feature b/middleman-more/features/asset_host.feature
index 00e52b59..30746473 100644
--- a/middleman-more/features/asset_host.feature
+++ b/middleman-more/features/asset_host.feature
@@ -1,7 +1,56 @@
 Feature: Alternate between multiple asset hosts
   In order to speed up page loading
-    
-  Scenario: Rendering html with the feature enabled
-    Given the Server is running at "asset-host-app"
+  
+  Scenario: Set single host globally
+    Given a fixture app "asset-host-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_host
+      set :asset_host, "http://assets1.example.com"
+      """
+    And the Server is running
     When I go to "/asset_host.html"
+    Then I should see "http://assets1"
+    When I go to "/stylesheets/asset_host.css"
+    Then I should see "http://assets1"
+
+  Scenario: Set proc host globally
+    Given a fixture app "asset-host-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_host
+      set :asset_host do |asset|
+        "http://assets%d.example.com" % (asset.hash % 4)
+      end
+      """
+    And the Server is running
+    When I go to "/asset_host.html"
+    Then I should see "http://assets"
+    When I go to "/stylesheets/asset_host.css"
+    Then I should see "http://assets"
+
+  Scenario: Set single host with inline-option
+    Given a fixture app "asset-host-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_host, :host => "http://assets1.example.com"
+      """
+    And the Server is running
+    When I go to "/asset_host.html"
+    Then I should see "http://assets1"
+    When I go to "/stylesheets/asset_host.css"
+    Then I should see "http://assets1"
+
+  Scenario: Set proc host with inline-option
+    Given a fixture app "asset-host-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_host, :host => Proc.new { |asset|
+        "http://assets%d.example.com" % (asset.hash % 4)
+      }
+      """
+    And the Server is running
+    When I go to "/asset_host.html"
+    Then I should see "http://assets"
+    When I go to "/stylesheets/asset_host.css"
     Then I should see "http://assets"
\ No newline at end of file
diff --git a/middleman-more/features/asset_host_compass.feature b/middleman-more/features/asset_host_compass.feature
deleted file mode 100644
index 7f477b63..00000000
--- a/middleman-more/features/asset_host_compass.feature
+++ /dev/null
@@ -1,7 +0,0 @@
-Feature: Alternate between multiple asset hosts
-  In order to speed up page loading
-  
-  Scenario: Rendering css with the feature enabled
-    Given the Server is running at "asset-host-app"
-    When I go to "/stylesheets/asset_host.css"
-    Then I should see "http://assets"
\ No newline at end of file
diff --git a/middleman-more/fixtures/asset-host-app/config.rb b/middleman-more/fixtures/asset-host-app/config.rb
index 8d363a55..e69de29b 100644
--- a/middleman-more/fixtures/asset-host-app/config.rb
+++ b/middleman-more/fixtures/asset-host-app/config.rb
@@ -1,6 +0,0 @@
-set :layout, false
-
-activate :asset_host
-set :asset_host do |asset|
-  "http://assets%d.example.com" % (asset.hash % 4)
-end
diff --git a/middleman-more/lib/middleman-more.rb b/middleman-more/lib/middleman-more.rb
index c4c771fe..df73efa9 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::Extension
+          Middleman::Extensions::AssetHash
         end
 
         # AssetHost allows you to setup multiple domains to host your static
diff --git a/middleman-more/lib/middleman-more/core_extensions/compass.rb b/middleman-more/lib/middleman-more/core_extensions/compass.rb
index e06380be..584f67a0 100644
--- a/middleman-more/lib/middleman-more/core_extensions/compass.rb
+++ b/middleman-more/lib/middleman-more/core_extensions/compass.rb
@@ -52,8 +52,14 @@ module Middleman
               # No line-comments in test mode (changing paths mess with sha1)
               compass_config.line_comments = false if ENV["TEST"]
 
-              if config.defines_setting?(:asset_host) && config[:asset_host].is_a?(Proc)
-                compass_config.asset_host(&config[:asset_host])
+              if extensions[:asset_host] && asset_host = extensions[:asset_host].host
+                if asset_host.is_a?(Proc)
+                  compass_config.asset_host(&asset_host)
+                else
+                  compass_config.asset_host do |asset|
+                    asset_host
+                  end
+                end
               end
             end
 
diff --git a/middleman-more/lib/middleman-more/extensions/asset_hash.rb b/middleman-more/lib/middleman-more/extensions/asset_hash.rb
index ca710a4b..93e86a06 100644
--- a/middleman-more/lib/middleman-more/extensions/asset_hash.rb
+++ b/middleman-more/lib/middleman-more/extensions/asset_hash.rb
@@ -1,119 +1,105 @@
 module Middleman
   module Extensions
-    module AssetHash
-      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"
+    class AssetHash < ::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
+      def initialize(app, options_hash={})
+        super
 
-          require 'digest/sha1'
-          require 'rack/test'
-          require 'uri'
-        end
-
-        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
+        require 'digest/sha1'
+        require 'rack/test'
+        require 'uri'
       end
 
-      # Central class for managing asset_hash extension
-      class AssetHashManager
-        def initialize(app, exts, ignore)
-          @app = app
-          @exts = exts
-          @ignore = ignore
-        end
+      def after_configuration
+        # Allow specifying regexes to ignore, plus always ignore apple touch icons
+        @ignore = Array(options.ignore) + [/^apple-touch-icon/]
 
-        # Update the main sitemap resource list
-        # @return [void]
-        def manipulate_resource_list(resources)
-          # 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
-            elsif %w(.js .css).include? a.ext
-              1
-            else
-              -1
-            end
-          end.each do |resource|
-            next unless @exts.include? resource.ext
-            next if @ignore.any? { |ignore| Middleman::Util.path_match(ignore, resource.destination_path) }
+        app.sitemap.register_resource_list_manipulator(:asset_hash, self)
 
-            # Render through the Rack interface so middleware and mounted apps get a shot
-            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
+        app.use Middleware, :exts => options.exts, :middleman_app => app, :ignore => @ignore
+      end
 
-            digest = Digest::SHA1.hexdigest(response.body)[0..7]
-
-            resource.destination_path = resource.destination_path.sub(/\.(\w+)$/) { |ext| "-#{digest}#{ext}" }
+      # Update the main sitemap resource list
+      # @return [void]
+      def manipulate_resource_list(resources)
+        # Process resources in order: binary images and fonts, then SVG, then JS/CSS.
+        # This is so by the time we get around to the text files (which may reference
+        # images and fonts) the static assets' hashes are already calculated.
+        rack_client = ::Rack::Test::Session.new(@app.class.to_rack_app)
+        resources.sort_by do |a|
+          if %w(.svg).include? a.ext
+            0
+          elsif %w(.js .css).include? a.ext
+            1
+          else
+            -1
           end
+        end.each do |resource|
+          next unless options.exts.include? resource.ext
+          next if @ignore.any? { |ignore| Middleman::Util.path_match(ignore, resource.destination_path) }
+
+          # Render through the Rack interface so middleware and mounted apps get a shot
+          response = rack_client.get(URI.escape(resource.destination_path), {}, { "bypass_asset_hash" => "true" })
+          raise "#{resource.path} should be in the sitemap!" unless response.status == 200
+
+          digest = Digest::SHA1.hexdigest(response.body)[0..7]
+
+          resource.destination_path = resource.destination_path.sub(/\.(\w+)$/) { |ext| "-#{digest}#{ext}" }
         end
       end
+    end
 
-      # The asset hash middleware is responsible for rewriting references to
-      # assets to include their new, hashed name.
-      class Middleware
-        def initialize(app, options={})
-          @rack_app        = app
-          @exts            = options[:exts]
-          @ignore          = options[:ignore]
-          @exts_regex_text = @exts.map {|e| Regexp.escape(e) }.join('|')
-          @middleman_app   = options[:middleman_app]
-        end
+    # The asset hash middleware is responsible for rewriting references to
+    # assets to include their new, hashed name.
+    class Middleware
+      def initialize(app, options={})
+        @rack_app        = app
+        @exts            = options[:exts]
+        @ignore          = options[:ignore]
+        @exts_regex_text = @exts.map {|e| Regexp.escape(e) }.join('|')
+        @middleman_app   = options[:middleman_app]
+      end
 
-        def call(env)
-          status, headers, response = @rack_app.call(env)
+      def call(env)
+        status, headers, response = @rack_app.call(env)
 
-          # We don't want to use this middleware when rendering files to figure out their hash!
-          return [status, headers, response] if env["bypass_asset_hash"] == 'true'
+        # We don't want to use this middleware when rendering files to figure out their hash!
+        return [status, headers, response] if env["bypass_asset_hash"] == 'true'
 
-          path = @middleman_app.full_path(env["PATH_INFO"])
-          dirpath = Pathname.new(File.dirname(path))
+        path = @middleman_app.full_path(env["PATH_INFO"])
+        dirpath = Pathname.new(File.dirname(path))
 
-          if path =~ /(^\/$)|(\.(htm|html|php|css|js)$)/
-            body = ::Middleman::Util.extract_response_text(response)
+        if path =~ /(^\/$)|(\.(htm|html|php|css|js)$)/
+          body = ::Middleman::Util.extract_response_text(response)
 
-            if body
-              # TODO: This regex will change some paths in plan HTML (not in a tag) - is that OK?
-              body.gsub! /([=\'\"\(]\s*)([^\s\'\"\)]+(#{@exts_regex_text}))/ do |match|
-                opening_character = $1
-                asset_path = $2
+          if body
+            # TODO: This regex will change some paths in plan HTML (not in a tag) - is that OK?
+            body.gsub!(/([=\'\"\(]\s*)([^\s\'\"\)]+(#{@exts_regex_text}))/) do |match|
+              opening_character = $1
+              asset_path = $2
 
-                relative_path = Pathname.new(asset_path).relative?
+              relative_path = Pathname.new(asset_path).relative?
 
-                asset_path = dirpath.join(asset_path).to_s if relative_path
+              asset_path = dirpath.join(asset_path).to_s if relative_path
 
-                if @ignore.any? { |r| asset_path.match(r) }
-                  match
-                elsif asset_page = @middleman_app.sitemap.find_resource_by_path(asset_path)
-                  replacement_path = "/#{asset_page.destination_path}"
-                  replacement_path = Pathname.new(replacement_path).relative_path_from(dirpath).to_s if relative_path
+              if @ignore.any? { |r| asset_path.match(r) }
+                match
+              elsif asset_page = @middleman_app.sitemap.find_resource_by_path(asset_path)
+                replacement_path = "/#{asset_page.destination_path}"
+                replacement_path = Pathname.new(replacement_path).relative_path_from(dirpath).to_s if relative_path
 
-                  "#{opening_character}#{replacement_path}"
-                else
-                  match
-                end
+                "#{opening_character}#{replacement_path}"
+              else
+                match
               end
-
-              status, headers, response = Rack::Response.new(body, status, headers).finish
             end
+
+            status, headers, response = Rack::Response.new(body, status, headers).finish
           end
-          [status, headers, response]
         end
+        [status, headers, response]
       end
     end
   end
diff --git a/middleman-more/lib/middleman-more/extensions/asset_host.rb b/middleman-more/lib/middleman-more/extensions/asset_host.rb
index deb708d3..8dfa4828 100644
--- a/middleman-more/lib/middleman-more/extensions/asset_host.rb
+++ b/middleman-more/lib/middleman-more/extensions/asset_host.rb
@@ -3,24 +3,19 @@ module Middleman
   module Extensions
 
     # Asset Host module
-    module AssetHost
+    class AssetHost < ::Middleman::Extension
+      option :host, nil, 'The asset host to use, or false for no asset host, or a Proc to determine asset host'
 
-      # Setup extension
-      class << self
+      def initialize(app, options_hash={}, &block)
+        super
 
-        # Once registered
-        def registered(app, options={})
-          app.config.define_setting :asset_host, false, 'The asset host to use, or false for no asset host, or a Proc to determine asset host'
+        # Backwards compatible API
+        app.config.define_setting :asset_host, nil, 'The asset host to use, or false for no asset host, or a Proc to determine asset host'
+        app.send :include, InstanceMethods
+      end
 
-          if options[:host]
-            config[:asset_host] = options[:host]
-          end
-
-          # Include methods
-          app.send :include, InstanceMethods
-        end
-
-        alias :included :registered
+      def host
+        app.config[:asset_host] || options[:host]
       end
 
       # Asset Host Instance Methods
@@ -32,13 +27,15 @@ module Middleman
         # @param [String] prefix
         # @return [String]
         def asset_url(path, prefix="")
-          original_output = super
-          return original_output unless config[:asset_host]
+          controller = extensions[:asset_host]
 
-          asset_prefix = if config[:asset_host].is_a?(Proc)
-            config[:asset_host].call(original_output)
-          elsif config[:asset_host].is_a?(String)
-            config[:asset_host]
+          original_output = super
+          return original_output unless controller.host
+
+          asset_prefix = if controller.host.is_a?(Proc)
+            controller.host.call(original_output)
+          elsif controller.host.is_a?(String)
+            controller.host
           end
 
           File.join(asset_prefix, original_output)