The RedRat core code and SDK have seen a major update so that both the .NET Framework and .NET Core are supported. This is to track Microsoft's road-map for multi-platform .NET, so that the same code can be run on Windows (.NET Framework), Linux and Mac (.NET Core).
At the moment most GUI based applications remain Windows only, but command line tools and web based applications (such as RedRatHub) are also being ported to .NET core for multi-platform operation.
The new core RedRat.dll is available via NuGet. More details and sample code available on the SDK page.