Corrected interface name.

Potentially breaking, but I highly doubt anyone implemented this interface.

src/Orchard.Web/Modules/Orchard.Layouts/Framework/Harvesters/IElementHarvester.cs

@@ -2,7 +2,7 @@
 using Orchard.Layouts.Framework.Elements;
 
 namespace Orchard.Layouts.Framework.Harvesters {
-    public interface ElementHarvester : ISingletonDependency {
+    public interface IElementHarvester : ISingletonDependency {
         IEnumerable<ElementDescriptor> HarvestElements(HarvestElementsContext context);
     }
 }

src/Orchard.Web/Modules/Orchard.Layouts/Orchard.Layouts.csproj

@@ -367,6 +367,7 @@
     <Compile Include="Helpers\PrefixHelper.cs" />
     <Compile Include="Helpers\JsonHelper.cs" />
     <Compile Include="Helpers\StringHelper.cs" />
+    <Compile Include="Providers\WidgetElementHarvester.cs" />
     <Compile Include="Recipes\Builders\CustomElementsStep.cs" />
     <Compile Include="Recipes\Executors\CustomElementsStep.cs" />
     <Compile Include="Providers\BlueprintElementHarvester.cs" />

src/Orchard.Web/Modules/Orchard.Layouts/Providers/BlueprintElementHarvester.cs

@@ -10,7 +10,7 @@ using Orchard.Layouts.Models;
 using Orchard.Layouts.Services;
 
 namespace Orchard.Layouts.Providers {
-    public class BlueprintElementHarvester : Component, ElementHarvester {
+    public class BlueprintElementHarvester : Component, IElementHarvester {
         private readonly Work<IElementBlueprintService> _elementBlueprintService;
         private readonly Work<IElementManager> _elementManager;
         private bool _isHarvesting;

src/Orchard.Web/Modules/Orchard.Layouts/Providers/ContentFieldElementHarvester.cs

@@ -13,7 +13,7 @@ using Orchard.Layouts.Helpers;
 using Orchard.Layouts.Services;
 
 namespace Orchard.Layouts.Providers {
-    public class ContentFieldElementHarvester : Component, ElementHarvester {
+    public class ContentFieldElementHarvester : Component, IElementHarvester {
         private readonly Work<IContentDefinitionManager> _contentDefinitionManager;
         private readonly Work<ITransactionManager> _transactionManager;
         private readonly Work<ICultureAccessor> _cultureAccessor;

src/Orchard.Web/Modules/Orchard.Layouts/Providers/ContentPartElementHarvester.cs

@@ -13,7 +13,7 @@ using Orchard.Layouts.Settings;
 using Orchard.Utility.Extensions;
 
 namespace Orchard.Layouts.Providers {
-    public class ContentPartElementHarvester : Component, ElementHarvester {
+    public class ContentPartElementHarvester : Component, IElementHarvester {
         private readonly Work<IContentDefinitionManager> _contentDefinitionManager;
         private readonly Work<IElementFactory> _elementFactory;
         private readonly Work<IElementManager> _elementManager;

src/Orchard.Web/Modules/Orchard.Layouts/Providers/SnippetElementHarvester.cs

@@ -16,7 +16,7 @@ using Orchard.Utility.Extensions;
 
 namespace Orchard.Layouts.Providers {
     [OrchardFeature("Orchard.Layouts.Snippets")]
-    public class SnippetElementHarvester : Component, ElementHarvester {
+    public class SnippetElementHarvester : Component, IElementHarvester {
         private const string SnippetShapeSuffix = "Snippet";
         private readonly Work<IShapeFactory> _shapeFactory;
         private readonly Work<ISiteThemeService> _siteThemeService;

src/Orchard.Web/Modules/Orchard.Layouts/Providers/TypedElementHarvester.cs

@@ -6,7 +6,7 @@ using Orchard.Layouts.Framework.Harvesters;
 using Orchard.Layouts.Services;
 
 namespace Orchard.Layouts.Providers {
-    public class TypedElementHarvester : ElementHarvester {
+    public class TypedElementHarvester : IElementHarvester {
         private readonly Work<IElementManager> _elementManager;
         private readonly Work<IElementFactory> _factory;
 

src/Orchard.Web/Modules/Orchard.Layouts/Providers/WidgetElementHarvester.cs

@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Orchard.ContentManagement.MetaData;
+using Orchard.ContentManagement.MetaData.Models;
+using Orchard.Core.Contents.Settings;
+using Orchard.Environment;
+using Orchard.Layouts.Framework.Display;
+using Orchard.Layouts.Framework.Elements;
+using Orchard.Layouts.Framework.Harvesters;
+using Orchard.Layouts.Services;
+using Orchard.Layouts.Settings;
+using Orchard.Utility.Extensions;
+
+namespace Orchard.Layouts.Providers {
+    public class WidgetElementHarvester : Component, IElementHarvester {
+        private readonly Work<IContentDefinitionManager> _contentDefinitionManager;
+        private readonly Work<IElementFactory> _elementFactory;
+        private readonly Work<IElementManager> _elementManager;
+
+        public WidgetElementHarvester(
+            Work<IContentDefinitionManager> contentDefinitionManager,
+            Work<IElementFactory> elementFactory,
+            Work<IElementManager> elementManager) {
+
+            _contentDefinitionManager = contentDefinitionManager;
+            _elementFactory = elementFactory;
+            _elementManager = elementManager;
+        }
+
+        public IEnumerable<ElementDescriptor> HarvestElements(HarvestElementsContext context) {
+            var elementType = typeof(Elements.ContentPart);
+            var contentPartElement = _elementFactory.Value.Activate(elementType);
+            var contentParts = GetContentParts(context);
+
+            return contentParts.Select(contentPart => {
+
+                var partSettings = contentPart.Settings.TryGetModel<ContentPartSettings>();
+                var partDescription = partSettings != null ? partSettings.Description : null;
+                var description = T(!String.IsNullOrWhiteSpace(partDescription) ? partDescription : contentPart.Name);
+                return new ElementDescriptor(elementType, contentPart.Name, T(contentPart.Name.CamelFriendly()), description, contentPartElement.Category) {
+                    Displaying = displayContext => Displaying(displayContext),
+                    ToolboxIcon = "\uf1b2",
+                    StateBag = new Dictionary<string, object> {
+                        {"ElementTypeName", contentPart.Name}
+                    }
+                };
+            });
+        }
+
+        private IEnumerable<ContentPartDefinition> GetContentParts(HarvestElementsContext context) {
+            var contentTypeDefinition = context.Content != null
+                ? _contentDefinitionManager.Value.GetTypeDefinition(context.Content.ContentItem.ContentType)
+                : default(ContentTypeDefinition);
+
+            var parts = contentTypeDefinition != null
+                ? contentTypeDefinition.Parts.Select(x => x.PartDefinition)
+                : _contentDefinitionManager.Value.ListPartDefinitions();
+
+            return parts.Where(p => p.Settings.GetModel<ContentPartLayoutSettings>().Placeable);
+        }
+
+        private void Displaying(ElementDisplayingContext context) {
+            var drivers = _elementManager.Value.GetDrivers(context.Element);
+
+            foreach (var driver in drivers) {
+                driver.Displaying(context);
+            }
+        }
+    }
+}

src/Orchard.Web/Modules/Orchard.Layouts/Services/ElementManager.cs

@@ -9,7 +9,7 @@ using Orchard.Layouts.Helpers;
 
 namespace Orchard.Layouts.Services {
     public class ElementManager : Component, IElementManager {
-        private readonly Lazy<IEnumerable<ElementHarvester>> _elementHarvesters;
+        private readonly Lazy<IEnumerable<IElementHarvester>> _elementHarvesters;
         private readonly ICacheManager _cacheManager;
         private readonly Lazy<IEnumerable<IElementDriver>> _drivers;
         private readonly Lazy<IEnumerable<ICategoryProvider>> _categoryProviders;
@@ -18,7 +18,7 @@ namespace Orchard.Layouts.Services {
         private readonly IElementEventHandler _elementEventHandler;
 
         public ElementManager(
-            Lazy<IEnumerable<ElementHarvester>> elementHarvesters,
+            Lazy<IEnumerable<IElementHarvester>> elementHarvesters,
             ICacheManager cacheManager,
             Lazy<IEnumerable<IElementDriver>> drivers,
             Lazy<IEnumerable<ICategoryProvider>> categoryProviders,