Program.cs

using System;
using System.Windows.Forms;
using System.Threading;
using System.Runtime.InteropServices;
using System.Diagnostics;


namespace ScpServer
{
    static class Program
    {
        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool SetForegroundWindow(IntPtr hWnd);

        [DllImport("user32.dll")]
        private static extern IntPtr GetForegroundWindow();

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            System.Runtime.GCSettings.LatencyMode = System.Runtime.GCLatencyMode.LowLatency;
            try
            {
                System.Diagnostics.Process.GetCurrentProcess().PriorityClass = System.Diagnostics.ProcessPriorityClass.High;
            }
            catch
            {
                // Ignore problems raising the priority.
            }
            bool createdNew = true;
            using (Mutex mutex = new Mutex(true, "MyApplicationName", out createdNew))
            {
                if (createdNew)
                {
                    Application.EnableVisualStyles();
                    Application.SetCompatibleTextRenderingDefault(false);
                    Application.Run(new ScpForm());
                }
                else
                {
                    Process current = Process.GetCurrentProcess();
                    foreach (Process process in Process.GetProcessesByName("DS4Windows"))
                    {
                        if (process.Id != current.Id)
                        {
                            SetForegroundWindow(process.MainWindowHandle);
                            if (GetForegroundWindow() != process.MainWindowHandle) //if tool is minimized to tray
                            {
                                Application.EnableVisualStyles();
                                Application.SetCompatibleTextRenderingDefault(false);
                                Application.Run(new Alreadyrunning());
                            }
                            break;
                        }
                    }
                }
            }
        }
    }
}