Orchard is a free, open source, community-focused project aimed at delivering applications and reusable components on the ASP.NET platform.
The Orchard project is focused on delivering a .NET-based CMS application that will allow users to rapidly create content-driven Websites, and an extensibility framework that will allow developers and customizers to provide additional functionality through modules and themes.
You can learn more about the project on the Orchard Project website.