gistfile1.cs

using System.ComponentModel;
using System.Windows.Forms;

namespace WindowsFormsApplication
{
    public class MainForm : Form
    {
        private IContainer components;
        private NotifyIcon notifyIcon;

        public MainForm()
        {
            this.InitializeComponent();

            this.notifyIcon = new NotifyIcon();
            this.notifyIcon.Click += (s, e) =>
            {
                this.WindowState = FormWindowState.Normal;
                this.notifyIcon.Visible = false;
            };

            this.ShowInTaskbar = false;
            this.ShowIcon = false;
            this.Resize += (s, e) =>
            {
                if (this.WindowState == FormWindowState.Minimized)
                {
                    this.notifyIcon.Visible = true;
                    this.notifyIcon.Icon = Properties.Resources.MyNotifyIcon;

                    this.WindowState = FormWindowState.Minimized;
                    this.ShowInTaskbar = false;
                }
            };
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                this.components.Dispose();
            }
            
            base.Dispose(disposing);
        }

        private void InitializeComponent()
        {
            this.components = new Container();
            this.AutoScaleMode = AutoScaleMode.Font;
            this.Text = "";
        }
    }
}