Doorstop X firewall is a firewall which protects your Mac from outside attacks.
Doorstop X Firewall provides critical improvements to OS Xs built-in firewall. Features include four protection modes (deny all, allow all, allow by address, deny by address) and full logging of allowed and/or denied connections.
Can be integrated with the Whos There? Firewall Advisor (also available for download on this site) to help you understand, analyze and react to access attempts.
The 30 day evaluation version is fully-functional. For Mac OS X 10.3.9 or later.