I just tested this modified script, which, when started, stays on top until YOU close it. Hope that that is what you wanted. If you close the Gui, the AHK script will close as well.
SetTitleMatchMode, 2
;:*:\lb::
Gui, Add, ListBox, h100 vLB, apple||bannana|cantaloup|kiwi|orange|pomegranate|strawberry
Gui, Add, Button, Default, Input
Gui, +AlwaysOnTop
Gui, Show
return
ButtonInput:
Gui, Submit, NoHide
;MsgBox, %LB%
ControlSend,, %LB%, Part of your App title in the windows bar OR ahk_class ABCD (via AHK Windows Spy)
Return
GuiClose:
GuiEscape:
Gui, Destroy
ExitApp
Update:
I could not help it, but had to add some more functionality. You can now double click on an item and it automatically moves to the next cell.
#SingleInstance Force
#installKeybdHook
#Persistent
Gui, Add, ListBox, h100 vMyListBox gMyListBox, apple|bannana|cantaloup|kiwi|orange|pomegranate|strawberry
Gui, Add, Button, Default, Input
Gui, +AlwaysOnTop
Gui, Show
return
MyListBox:
if A_GuiControlEvent <> DoubleClick
return
GuiControlGet, MyListBox ; Retrieve the ListBox's current selection.
Send, !{Esc}
Sleep, 200
SendInput, %MyListBox%{Tab}
return
ButtonInput:
Gui, Submit, NoHide
Send, !{Esc}
Sleep, 200
SendInput, %MyListBox%{Tab}
Return
GuiClose:
GuiEscape:
Gui, Destroy
ExitApp