C#

// Form1.cs
using System;
using System.Windows.Forms;
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        Shown += new EventHandler(Form1_Shown);
    }
    void Form1_Shown(object sender, EventArgs e)
    {
        Form2 form2 = new Form2();
        form2.TextUpdated += new EventHandler<TextUpdatedEventArgs>(form2_TextUpdated);
        form2.Show();
    }
    void form2_TextUpdated(object sender, TextUpdatedEventArgs e)
    {
        // Do your thing here
        Console.WriteLine(e.Text);
    }
}

// Form2.cs
using System;
using System.Windows.Forms;
public partial class Form2 : Form
{
    public event EventHandler<TextUpdatedEventArgs> TextUpdated;
    public Form2()
    {
        InitializeComponent();
    }
    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        OnTextUpdated(new TextUpdatedEventArgs(textBox1.Text));
    }
    protected virtual void OnTextUpdated(TextUpdatedEventArgs e)
    {
        EventHandler<TextUpdatedEventArgs> eh = TextUpdated;
        if (eh != null)
            eh(this, e);
    }
}

// TextUpdatedEventArgs.cs
using System;
public class TextUpdatedEventArgs : EventArgs
{
    private string m_Text;
    public TextUpdatedEventArgs(string text)
    {
        m_Text = text;
    }
    public string Text
    {
        get { return m_Text; }
    }
}

static void Main(string[] args) {
	foreach (string line in File.ReadAllLines(args[0]+".gpl")) {
		switch (line.Substring(0,Math.Min(line.Length,4))) {
			case "out ": Console.WriteLine(line.Substring(4)); break;
			case "time": Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")); break;
			case "end.": return;
			default: Console.WriteLine("Syntax error."); return;
		}
	}
}

out Hello
out World!
time
end.

Hello
World!
2009-02-11 18:48:49

Form1 form1 = new Form1;
Form2 form2 = new Form2;
Form3 form3 = new Form3;
...

private static void HideAll()
{
if(form1 != null && !form1.Disposed && form1.Visible)
   form1.Hide();
...
}

public static void ShowForm(int formNum)
{
HideAll();
switch(formNum)
{
  case 1:
      form1.Show();
  break;
  ...
}
}

StaticForm.ShowForm(1);//to show Form1 only

using WindowsApplication8;

public partial class Form1 : Form
    {
        WindowsApplication8.Form2 f2;
}

 private void ll_linkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
             //System.Diagnostics.Process.Start("Form2.cs");
             //f2 = new Form2();
         //f2.showDialog();   

             f2 = new WindowsApplication8.Form2();
             //f2.Activate();
             f2.Show();
            
            
        }