DotNetNuke Platform (formerly DotNetNuke Community Edition) is a popular open source ASP.NET based Content Management System. It can be easily customized using themes.
Moreover, you can extend the functionality of your site using modules. DotNetNuke itself ships with several modules but you can purchase advanced third party modules to deliver rich user experience.
In this video, you will learn the steps required to install DotNetNuke using web app gallery included with WebsitePanel.