Orchard is a free, open source, community-focused Content Management System built on the ASP.NET MVC platform.
Orchard is built on a modern architecture that puts extensibility up-front, as its number one concern. All components in Orchard can be replaced or extended. Content is built from easily composable building blocks. Modules extend the system in a very decoupled fashion, where a commenting module for example can as easily apply to pages, blog posts, photos or products. A rich UI composition system completes the picture and ensures that you can get the exact presentation that you need for your content.