The origin of DotNetNuke was a project by Microsoft called IbuySpy, from which this excellent CMS, the development of which started together with .NET, emerged. As well as a very advanced user management system, it's possible to create various portals with a unique installation both via intranets as well as on the Internet. And of course, it works over many of the state-of-the-art Microsoft technologies, like ASP.NET 2.0, VWD, Visual Studio or SQL Server.
The features of DotNetNuke allow it to manage several websites, designs, contents, security, users and members... All of which are totally customizable and use a really modern and functional interface.
All in all, if you want to manage your own website in a 100% Windows environment, DotNetNuke can be a good choice.