[Zope] which platform independent database?

Hi all, Does somebody know some free database and free database adapter for Zope, which exists for Linux and for windows too, please? Do you know some pros/cons and some wiev from praxis for that? I know, Gadfly, but this is really tiny, with problematic backup (need to disconnect, make backup and connect), sometimes it make mishmash in datafiles and then you need your backup... Many thanks, J. Lukesh