KillAllGUI.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Kill_GUI
{
    class Program
    {
        static void Main(string[] args)
        {
            foreach (Process p in Process.GetProcesses(System.Environment.MachineName))
            {
                if (p.MainWindowHandle != IntPtr.Zero)
                {
                    p.Kill();
                }
            }
        }
    }
}