Umbraco is an open-source content management system based on C# .Net. It usually uses a Microsoft SQL Database but it is possible to add a custom connection string.
Almost every aspect of umbraco can be changed, hooked into or overridden. If you are a good programmer and your page needs a lot of custom features, this is the perfect CMS for you. For a "normal" website or somebody who doesn't feel comfortable with MVC programming there might be better alternatives.
It doesn't have all the features of sitecore but it is free!