SO / SE is one of the posterchild of C# / .Net. However at the beginning they were really Windows only while now there's really a lot of Linux in there. HAProx

SO / SE is one of the posterchild of C# / .Net. However at the beginning they were really Windows only while now there's really a lot of Linux in there. HAProxy running on Linux, for example. There was a recent post about the various technologies using by the entire stack and there have also been SO/SE employees detailing the stack here on HN. So it depends what you mean by "runs on Windows". Certainly the scalability issues are handled, at least in part, by Linux.