Umbraco

umbraco is an ASP.Net open-source Content Management System (CMS)(written in C#).
umbraco is optimized for the presentation of human-readable and human-editable website content. It is a completely customizable system - in other words, YOU CAN DO ANYTHING with umbraco, it's just a matter of how and if you need to use technologies outside of the basic umbraco framework.
umbraco is written using ASP.Net technology, but to create a website in umbraco you don't need to know anything about programming in ASP.Net, or C#. You can create your entire website in umbraco's web-based interface.

Go to http://www.umbraco.net/

See also these related projects.