There is no explicit commercial license. But if we knew what you want to do with the PunBB code we could offer such a license. Please, send me a PM or email with the description of your project (or how you want to use the PunBB code).
I do not want to use PunBB code.
I have some project's sources where PunBB is used as a forum base (avatars/authenticate module is rewritten at least) and I want to check is GPL license of PunBB enough to be sure that full sources are GPLed (there is no any other license info except PunBB part).
So as I understand by other legal checks - it has been used under usual GPL.
Usual copyright is in that sources:
/***********************************************************************
Copyright (C) 2002-2005 Rickard Andersson (rickard@punbb.org)
This file is part of PunBB.
PunBB is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 2 of the License,
or (at your option) any later version.
PunBB is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston,
MA 02111-1307 USA
************************************************************************/