Blackmire is a tool that uses Roslyn to convert C# code into C++ code. Simple as that. At the moment, Blackmire is a WPF application that allows the users to enter C# and shows C++ output in two panes: one for header and one for the implementation
Blackmire is currently at a very early stage. Declarations are processed, but definitions (i.e., what's inside methods) will in most cases yield junk.
Pull requests are your friend.