...
Migration Rules Files (mig Files) are the preferred means of mapping a COM API to its replacement in .NET. See
See Using Mig.IDF Files for COM API replacement
...
Custom IDFs allow you to migrate COM APIs to .NET replacements. This is a powerful and fairly intuitive technique, but it is not good usable as mig files.
The gmStudio samples use custom IDFs files, but this approach will be phased out in favor of using mig files. See Custom COM Replacement.
...
gmSL scripts may be used to implement dynamic translation rules for various COM migrations in concert with custom IDFs. gmSL Scripts may also be used for special purpose analysis and transformation on their own.
Note also that there is a .NET API that has all of the power of gmSL and may be used to build customer translation engines.
Learn more about gmsl here: gmSLIntroduction.
...