Last week I watched some videos about ASP.NET MVC. Rob Conery creates in episode 11 of the "ASP.NET MVC Storefront" series an ASP.NET MVC Component. Using components you can call an action method of a ComponentController and insert the rendered result into the view. Mike Bosch explains this concept in a blog post.
In ASP.NET MVC Preview 4 ComponentController has been removed and the method RenderComponent which called the ComponentController action from the view has been replaced by the method RenderAction which can call an action of a normal Controller. Since this concept conflicts with "Separation of concerns", Microsoft doesn't intend to include this feature in the RTM version of ASP.NET MVC.
ASP.NET MVC Futures
Therefore the ASP.NET MVC team moved the RenderAction method to the ASP.NET MVC Futures which consist of the assembly Microsoft.Web.Mvc.dll. This assembly contains features and prototypes which haven't been included in the RTM version yet. The release for ASP.NET MVC Beta 1 can be downloaded from Codeplex.
In order to use ASP.NET MVC Futures in your MVC project reference the assembly "Microsoft.Web.Mvc.dll" and insert the following line into the web.config to include the namespace "Microsoft.Web.Mvc" in all your views automatically:
SubControllers from MvcContrib
SubControllers can be used for similar purposes like RenderAction or Components. Matt Hinze presented this feature from the MvcContrib project in a blog post. SubController actions can be included in the view data as delegates. The views can then invoke these delegates and start the rendering of the SubController action view.
The host controller can pass objects to the SubController. Matt Hinze explains this feature in another blog post.