Maybe this works for killing on Windows

lib/apprunner.exs

@@ -38,7 +38,7 @@ defmodule MBU.AppRunner do
   end
 
   def kill(pid) do
-    System.find_executable("kill") |> System.cmd([pid])
+    os_kill(pid, :os.type())
   end
 
   def wait_loop(port) do
@@ -83,7 +83,7 @@ defmodule MBU.AppRunner do
         # screen and also redirects stdout properly. Without this flag, stdout
         # is not passed back to BEAM and cannot be logged.
         :hide,
-        
+
         args: real_args,
         line: 1024
       ]
@@ -101,6 +101,14 @@ defmodule MBU.AppRunner do
       ]
     )
   end
+
+  defp os_kill(pid, {:win32, _}) do
+    System.find_executable("cmd") |> System.cmd(["/c", "taskkill", "/PID", pid, "/F"])
+  end
+
+  defp os_kill(pid, _) do
+    System.find_executable("kill") |> System.cmd([pid])
+  end
 end
 
 [program | args] = System.argv()