Composite C1 is a free open source content management system based on the Microsoft .NET 4 platform.
Composite C1 allows companies and organizations, individuals or communities of users to easily publish, manage and organize a wide variety of content on a website. With Composite C1 you have the freedom to choose and switch between a free open source licence or a paid subscription model. Composite C1 is:

A professional fully featured CMS
Simple to extend and customize
Based on the latest Microsoft technology
Developed by and for professional web developers
Succesfully powering numerous corporate web sites
Based on a developer model and licence options that prevents vendor lock-in and secures your independence
Easy on the editor
The user interface is task oriented and enable newcomers to maintain the website content on a daily basis while making it possible for the experienced editor to control the corporate webexperience.

In Control -down to the last detail
Frontend and XSLT developers are able to control website look and feel in detail and are treated with the technical respect they deserve. .NET developers have access to the latest technologies, .NET 4, ASP.NET 4 Controls, ASP.NET MVC, pure LINQ data access, Workflow Foundation, a pluggable architecture and a documented API. If you need the complete source code for Composite C1, it’s licensed under MPL 1.1 and available at http://compositec1.codeplex.com/.

Simple business model: One edition – dual licenses
Composite C1 is distributed for free, and the Open Source licensed version is 100 % identical with the commercially licensed version, giving you the freedom to change your mind and avoid vendor lock-in. In addition to a commercial licence that gives companies benefits like product warranty, Composite also offers professional services like support, training, upgrade tools and commercially oriented modules.