Probably not, the language and most core libraries are supported by Mono, but things like WPF etc, are windows only. So unless your Windows app is in GTK#, you

Probably not, the language and most core libraries are supported by Mono, but things like WPF etc, are windows only. So unless your Windows app is in GTK#, you won't be able to help them. Saying that C# is multiplatform is like saying that Objective-C is, it's true technically, but having an app that run on both platform is a PITA because most libraries are not cross platform.