scripting-interface

How do I get started designing and implementing a script interface for my .NET application? There is VSTA (the .NET equivalent of VBA for COM ), but as far as I understand I would have to pay a license fee for every installation of my application. It is an open source the application so this will not work. There is also e.g. the embedding of interpreters (IronPython?), but I don't understand how this would allow exposing an "object model" (see below) to external (or internal) scripts. Sub-questions: What is the scripting interface story in .NET? Is it somehow trivial to do this in .NET? E.g.