Открытые окна и Фокус

    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool ShowWindow(IntPtr hWnd, ShowWindowCommand nCmdShow);
 
    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool SetForegroundWindow(IntPtr hWnd);

var openedWins = new List<Process>();
foreach(var proc in Process.GetProcesses())
    if (proc.MainWindowHandle != IntPtr.Zero && proc.MainWindowTitle.Length != 0)
        openedWins.Add(proc);
 
string @out = null;
foreach(var win in openedWins)
    @out += win.MainWindowTitle + "\r\n";
 
MessageBox.Show(@out);

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
 
namespace TestApplication
{
 
    public partial class Form1 : Form
    {
 
        
        public Form1()
        {
            InitializeComponent();
            var openedWins = new List<Process>();
            foreach (var proc in Process.GetProcesses())
                if (proc.MainWindowHandle != IntPtr.Zero && proc.MainWindowTitle.Length != 0)
                    openedWins.Add(proc);
            string @out = null;
            foreach (var win in openedWins)
                @out += win.MainWindowTitle + "\r\n";
        }
    }
}

using System.Diagnostics;

private static extern bool ShowWindow(IntPtr hWnd, ShowWindowCommand nCmdShow);