Make a window become the active window.

	// Draws 2  windows and when clicked on 1 window's button
	// Focus the other window.
	
	private var windowRect : Rect = Rect (20, 20, 120, 50);
	private var windowRect2 : Rect = Rect (20, 80, 120, 50);
	
	function OnGUI () {
		windowRect = GUI.Window (0, windowRect, DoMyFirstWindow, "First");
		windowRect2 = GUI.Window (1, windowRect2, DoMySecondWindow, "Second" );
	}
	
	function DoMyFirstWindow (windowID : int) {
		if (GUI.Button (Rect (10,20,100,20), "Focus other"))
			GUI.FocusWindow(1);
	}
	
	function DoMySecondWindow (windowID : int) {
		if (GUI.Button (Rect (10,20,100,20), "Focus other"))
			GUI.FocusWindow(0);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    private Rect windowRect = new Rect(20, 20, 120, 50);
    private Rect windowRect2 = new Rect(20, 80, 120, 50);
    void OnGUI() {
        windowRect = GUI.Window(0, windowRect, DoMyFirstWindow, "First");
        windowRect2 = GUI.Window(1, windowRect2, DoMySecondWindow, "Second");
    }
    void DoMyFirstWindow(int windowID) {
        if (GUI.Button(new Rect(10, 20, 100, 20), "Focus other"))
            GUI.FocusWindow(1);
        
    }
    void DoMySecondWindow(int windowID) {
        if (GUI.Button(new Rect(10, 20, 100, 20), "Focus other"))
            GUI.FocusWindow(0);
        
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	private windowRect as Rect = Rect(20, 20, 120, 50)

	private windowRect2 as Rect = Rect(20, 80, 120, 50)

	def OnGUI() as void:
		windowRect = GUI.Window(0, windowRect, DoMyFirstWindow, 'First')
		windowRect2 = GUI.Window(1, windowRect2, DoMySecondWindow, 'Second')

	def DoMyFirstWindow(windowID as int) as void:
		if GUI.Button(Rect(10, 20, 100, 20), 'Focus other'):
			GUI.FocusWindow(1)

	def DoMySecondWindow(windowID as int) as void:
		if GUI.Button(Rect(10, 20, 100, 20), 'Focus other'):
			GUI.FocusWindow(0)