Yes, WinpkFilter package has an interface for C# as well as C# basic samples.
Does a .NET version of the Internet Gateway sample application exist?
Regretfully only C++ version of Internet Gateway is available.
We need the functionality of the PassThru & Gateway samples but we also need to understand what we are doing a bit more. The goal is to add additional filtering rules in the future.
There is a C# PassThru sample in the package and it may the a good start point to grasp the basics of WinpkFilter. Internet Gateway only adds GUI interface and basic NAT functionality. Also, I can add that WinpkFilter has built-in filters, the sample code is available in filters.cpp, C++ version only but it is very simple and easy to understand.