Tcl/Tk has 'tile', which brings not only native look-and-feel to Tk, but also a possibility to change skin very easy; see http://mini.net/tcl/11075

You access Tcl/Tk using CPAN module Tcl::Tk

addition: non-rectangular windows are also available with this approach, see http://mini.net/tcl/13409, it explains how to achieve "Managed and shaped toplevel", and you can use this from Perl also...