Comodo Personal FW is free.
1 of comodo's internet security products is free; the other is commercial; each with a free download, but the C IS Pro has a 30 day trial period.
Comodo product comparisons.
http://www.personalfirewall.comodo.com/
Comodo Free product info.
http://www.personalfirewall.comodo.c..._firewall.html
Be aware that C IS can be installed as AV plus FW, AV only, FW only.
If you install Comodo's AV, do NOT install NOD32 or any other AV program.
I have no experience with NOD32.
Some companies have, recently, begun advertising a free download, which means that you do not have to pay them to download the program. But that might have no relationship to the use of the file you downloaded. Don't ask me. I wasn't in the meetings.
FWIW:
I stopped using C P FW because it tried to take control of too many aspects of my computer. I like to be in charge. Merely a personal choice. I know that many TGF members use Comodo products.
RF123