DNN (formerly DotNetNuke) is a web content management system based on Microsoft .NET. The DNN Platform Edition is open source.
DNN is written in C#, though it existed for many years as a VB.NET project. It is distributed under both a Community Edition MIT license and commercial proprietary licenses as DNN Evoq Content and DNN Evoq Engage editions.
Read more on http://www.dnnsoftware.com/platform