S#

"Beyond that, you can perform operations impossible in VB.NET or C#. For example, you can inherit sealed classes, such as System.String, and extend them to meet your needs. You can call external DLLs—not just ActiveX DLLs, or Win32 APIs, but any external DLL. You can dynamically add methods, properties, and fields to existing classes exposed by an assembly. "
[DevX]

Interesting...