I was thinking Tk all the way, until I hit "zoom all 20 windows together". If you need zooming, use Tk::Zinc (which allows you to zoom whole groups together) or Gtk2's Gnome2::Canvas ( which has a nice dynamic "pixels per unit" setting).

In Tk terms, you probably want to stack 20 Scrolled Canvases into a Scrolled Pane. There may be expansion problems with a complex pack like that, so you "may" need to fiddle with putting each Scrolled Canvas, into it's own Frame before packing into the Scrolled Pane. As always, the devil is in the details.