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I use Outpost 6.5.1 free. When you mention mode, do you mean so that it Auto creates rules? Or some other setting. Good to know you rate it so highly. Is there a version 7 free?
Well the free version is limited in its settings levels, but the Rules Wizard is the median level and the one which includes auto rules creation.
Since the introduction of Outpost 7, there is no free stand alone firewall version, but there is a free suite, which could conflict with avast. But if you have avast installed first before installing Outpost 7.1 free Suite it detects avast and asks for confirmation you installed it. When you confirm you have installed avast it will drop the anti-virus/spyware module so it shouldn't conflict.
http://free.agnitum.com/If you chose that you should ideally do a clean install of the outpost suite (uninstall existing free outpost, reboot, install outpost free suite) so it doesn't pick-up and old settings/configuration/