How can I drag a window if it doesn’t have a title bar or border

You can drag such a window by using Win32 APIs to switch the mouse hit to WM_NCLBUTTONDOWN. The code below will allow you to drag by mousing down anywhere in the form’s clientarea as long as you don’t hit a child control on the form.

	using System.Runtime.InteropServices;
	............
	public const int WM_NCLBUTTONDOWN = 0xA1; 
 	public const int HTCAPTION = 0x2; 
 
 	[DllImportAttribute ('user32.dll')] 
 	public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam); 
 
	[DllImportAttribute ('user32.dll')] 
	public static extern bool ReleaseCapture(); 

	private void Form2_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
	{
		ReleaseCapture();
		SendMessage(Handle, WM_NCLBUTTONDOWN, HTCAPTION, 0);
	}

Here is a solution posed by Jacob Grass (Abiliti Solutions) that does not rely on InteropServices.

	Private blnMoving As Boolean = False
	Private MouseDownX As Integer
	Private MouseDownY As Integer
 
	Private Sub Form1_MouseDown(ByVal sender As Object, _
    			ByVal e As System.Windows.Forms.MouseEventArgs) Handles Form1.MouseDown
    		If e.Button = MouseButtons.Left Then
			blnMoving = True
			MouseDownX = e.X
			MouseDownY = e.Y
		End If
	End Sub
 
	Private Sub Form1_MouseUp(ByVal sender As Object, _
			ByVal e As System.Windows.Forms.MouseEventArgs) Handles Form1.MouseUp
		If e.Button = MouseButtons.Left Then
			blnMoving = False
		End If
	End Sub
 
	Private Sub Form1_MouseMove(ByVal sender As Object, _
			ByVal e As System.Windows.Forms.MouseEventArgs) Handles Form1.MouseMove
		If blnMoving Then
			Dim temp As Point = New Point()
 
			temp.X = Form1.Location.X + (e.X - MouseDownX)
			temp.Y = Form1.Location.Y + (e.Y - MouseDownY)
			Form1.Location = temp
		End If
	End Sub