DotNetNuke is the leading Web Content Management Platform for Microsoft .NET. Our open platform allows you to quickly, inexpensively change the appearance or functionality of your web site by installing software add-ons. More than 8,000 third-party add-ons are available through our Snowcovered.com online marketplace, free add-ons are available in the standard install package or from the DotNetNuke Forge, and the open API enables you to create your own custom add-ons.
The open platform allows DotNetNuke to function as both a content management system (CMS) and application development framework. DotNetNuke allows your organization to leverage your existing Microsoft investments to create rich, highly interactive web sites and web applications.
DotNetNuke is available as a free Community Edition or as subscription services with more features as the Professional Edition and Enterprise Edition.
Video Introduction to DotNetNuke

Download the DotNetNuke Community Edition Using the Microsoft Web Platform Installer
DotNetNuke is the leading Web Content Management Platform for Microsoft ASP.NET