Download the current release of the DoorStop X Firewall

Open Door Networks 
Protects your Mac from outside attack
Easy-to-use interface means less chance of mistakes
Critical improvements to OS X's "built-in" firewall
Available standalone or as part of our integrated Security Suite
  Suite icon

You can download an evaluation version of the DoorStop X Firewall below. The current version of DoorStop X is 2.2 and requires Mac OS X 10.3.9 or later. It has been upgraded to fully support Leopard (Mac OS X 10.5), adding support for Leopard's many new and changed networking features. The evaluation version of DoorStop X is fully functional and will run for 30 days before expiring. If you are using a previous version of DoorStop X, DoorStop X 2.2 will utilize your current protection settings and preferences.

DoorStop icon
Download the DoorStop X Firewall

You can download other products from the DoorStop X Security Suite, or the whole Suite, here.