Sandcastle is a free Microsoft tool that automatically generates documentation from program source assemblies and XML comment files for Microsoft Visual Studio .NET development projects. The latest version of Sandcastle 2.7.2 from Microsoft is included with Help+Manual, making it possible to generate source code documentation from your .NET projects directly.
See the Source Code Documentation with Sandcastle chapter for full instructions on using Sandcastle for documenting your .NET source code.
Please note that you cannot use the independent Sandcastle Help File Builder system or its configuration. Help+Manual actually performs similar tasks to Help File Builder, so it replaces its role in interaction with Sandcastle.