System.MarshalByRefObject (class)

System.MarshalByRefObject derives from System.Object

System.MarshalByRefObject is the base class for objects that need to marshal their data across application boundaries.

Objects that don't inherit from System.MarshalByRefObject are able to marshal their data by value.

Two prominent classes that derives from MarshalByRefObject are System.__ComObject and System.AppDomain.