To get the text of an external window you could use the GetForegroundWindow and the GetWindowTextAPI functions. Here is a small example of its usage:

public partial class Form1 : Form    {        [DllImport("user32.dll")]        static extern int GetForegroundWindow();        [DllImport("user32.dll")]        static extern int GetWindowText(int hWnd, StringBuilder text, int count);         //Use SetWindowPos to make app alwaysontop        public Form1()        {            InitializeComponent();        }        private void GetActiveWindow()        {            const int nChars = 256;            int handle = 0;            StringBuilder Buff = new StringBuilder(nChars);            handle = GetForegroundWindow();            if (GetWindowText(handle, Buff, nChars)  0)            {                this.captionWindowLabel.Text = Buff.ToString();                this.IDWindowLabel.Text = handle.ToString();            }        }        private void timer1_Tick(object sender, EventArgs e)        {            GetActiveWindow();        }    }