class Win32
    {
        public const long WS_EX_TOOLWINDOW = 0x00000080L;
        public const long WS_EX_APPWINDOW = 0x00040000L;
    }
 
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        protected override CreateParams CreateParams {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= (int)Win32.WS_EX_TOOLWINDOW;
                cp.ExStyle -= (int)Win32.WS_EX_APPWINDOW;
                return cp;
            }
        }
    }