The tool ships with a handful of DLLs:
Directory of C:\Program Files (x86)\GreatMigrations\gmStudio\support\metalang
ASPGlobalIncludes.dll
CodeStyle.dll
lobSubsystem.dll
locSubsystem.dll
Migration.dll
MscomctlMigration.dll
ScrrunMigration.dll
The last two are loaded from the custom IDFs to help do deeper migrations.
C:\Program Files (x86)\GreatMigrations\gmStudio\support\rules\GM.MSCOMCTL.OCX.xml (1 hit)
Line 1906: <Refactor id="[GM.mscomctl.ocx]" dllName="MscomctlMigration.dll" event="mscomctl">
C:\Program Files (x86)\GreatMigrations\gmStudio\support\rules\GM.scrrun.dll.xml (1 hit)
Line 375: <Refactor id="[GM.scrrun.dll]" dllName="ScrrunMigration.dll" event="scrrun" >
They could probably be implemented using gmsl, but gmSL was not available when we implemented the DLLs, so the DLLs are still used.
The other DLLs are used for new, specialized, and undocumented features of the application.
We have plans to a C#-based extension SDK, but no release date is set.