A polyglot batch file/JScript.net application that listens on a port. Try it with `polyglot-listener.bat 1234` to listen on port 1234

polyglot-listener.bat

@if (@X)==(@Y) @end /* JScript comment
@echo off
REM Polyglot code adapted from https://stackoverflow.com/a/24396149/591064
setlocal enableDelayedExpansion

REM Too few arguments?
if "x%1" == "x" goto usage_help

REM Find the latest JScript.Net compiler
for /f "tokens=* delims=" %%v in ('dir /b /s /a:-d /o:-n "%SystemRoot%\Microsoft.NET\Framework\*jsc.exe"') do (
   set "jsc=%%v"
)

REM Always rebuild
IF exist %APPDATA%\listener.exe del %APPDATA%\listener.exe

echo.Compiling the listener script using !jsc!
"!jsc!" /nologo /out:"%APPDATA%\listener.exe" "%~dpsfnx0"

IF exist %APPDATA%\listener.exe (
    echo.Binary saved as %APPDATA%\listener.exe
    echo.Launching the listener on %2 %1
    start "Dummy server on TCP port %1" %APPDATA%\listener.exe %*
) else (
    echo.Unable to build polyglot code
)

goto end_of_batch_file

:usage_help
echo.Usage:
echo.   %0 port [ip]

:end_of_batch_file
endlocal & exit /b %errorlevel%

*/
import System;
import System.Net;
import System.Net.Sockets;
import System.Text;

function StartListening(port, ipAddress:IPAddress) {
   // Establish the local endpoint for the socket.
   // Dns.GetHostName returns the name of the host running the application.
   var localEndPoint = new IPEndPoint(ipAddress, parseInt(port));  

   // Create a TCP/IP socket.  
   var listener = new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp );  

   // Bind the socket to the local endpoint and listen for incoming connections.  
   try {  
       listener.Bind(localEndPoint);  
       listener.Listen(10);  

       // Start listening for connections.  
       while (true) {  
           // Data buffer for incoming data.  
           var data:byte[] = new byte[1024];

           Console.WriteLine("Waiting for a TCP connection on {0}:{1}...", ipAddress, port);  
           var handler = listener.Accept();  

           Console.WriteLine("Connected to {0}", handler.RemoteEndPoint);  

           try {
               while (handler.Receive(data) > 0);  
            } finally {
               Console.WriteLine("Disconected\n");
            }

           handler.Shutdown(SocketShutdown.Both);  
           handler.Close();  
       }  

   } catch (e) {  
       Console.WriteLine(e.ToString());  
   }  
}

function GetThisHostIPv4Address() {
   var ipAddress = IPAddress.Parse("127.0.0.1");  // Default to localhost
   var ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());  

   //Let's see if we have something in the DNS that looks like
   //an IPv4 address
   for(var i=0; i<ipHostInfo.AddressList.length; ++i) {
       if (ipHostInfo.AddressList[i].AddressFamily == AddressFamily.InterNetwork) {
          ipAddress = ipHostInfo.AddressList[i];
          break;
        }
   }

   return ipAddress;
}

//----- MAIN ---------
var arguments:String[] = Environment.GetCommandLineArgs();

if (arguments.length == 2) {
    StartListening(arguments[1], GetThisHostIPv4Address());
} else if (arguments.length == 3) {
    StartListening(arguments[1], IPAddress.Parse(arguments[2]));
} else {
    Console.WriteLine("Usage: listener port [ip]");
}