Use Lambda Expressions as Unmanaged Callbacks

// Even more simplified
class Program
{
    [DllImport("user32", ExactSpelling = true)]
    static extern bool EnumWindows(WNDENUMPROC lpEnumFunc, IntPtr lParam);

    [UnmanagedFunctionPointer(CallingConvention.Winapi)]
    delegate bool WNDENUMPROC(IntPtr hwnd, IntPtr lParam);

    static void Main(string[] args)
    {
        List<IntPtr> windows = new List<IntPtr>();
        EnumWindows((hwnd, lParam) =>
        {
            windows.Add(hwnd);
            return true;
        }, IntPtr.Zero);
    }
}