Visual Studio Tools for Applications
Visual Studio Tools for Applications (VSTA) is a set of tools that independent software vendors (ISVs) can use to build customization abilities into their applications for both automation and extensibility. Those customization abilities can be used by end-users to tailor the ISV's application within a managed extensibility environment just like Visual Basic for Applications.
Source: Wikipedia — Visual Studio Tools for Applications (CC BY-SA 4.0)