using System.Diagnostics; class Program { static void Main() { if (TestIfAlreadyRunning()) { System.Console.WriteLine("This app is already running!"); } else { // Here, the entry point of the application. } } static bool TestIfAlreadyRunning() { Process processCurrent = Process.GetCurrentProcess(); Process[] processes = Process.GetProcesses(); foreach (Process process in processes) { if (processCurrent.Id != process.Id) { if (processCurrent.ProcessName == process.ProcessName) { return true; } } } return false; } }