well, if this works out, all the libraries in pure C#. (actually not just C# but F#, Nemerle, VB.net, all the dotnet languages should work with an extra step though dynamic ones probably won't work or won't work easily. like ironpython)
it's a source to source transpiler. The C# programs should also work. one can also use it to make his/her C# program faster, assuming Nim code is faster than c#'s dotnet, that is.