Modifier with Visual Basic for Applications
This gives you the ability to modify screens in Dynamics GP: hide fields, rename fields, add fields, etc.. It also gives you the ability to create your own customizations using visual basic for applications code.
You don't have to own this module merely to run some VBA customizations that someone else has created for you (i.e. if your local Dynamics GP partner builds something for you). This is required if you want to be able to build and/or edit your own code.