Is there an ASP.NET MVC portal that is either commercially available or open source?
I am defining a portal as a content management system (CMS) where I can develop modules that can run from within the portal. Examples are DotNetNuke, Mojo Portal, Drop Things, and Rainbow portal.
As far as I know Stack Overflow and Server Fault are both done with ASP.NET MVC. 😉
And if by “portal” you mean “platform” like DotNetNuke, the only thing which comes to my mind is Stack Exchange.
Also you can check: