I've been using Kerio Personal Firewall 2.1.5 from Kerio Technologies on a Windows 98 Second Edition (SE) system. I hadn't use the system for quite awhile. When I did so today, I checked on whether an update was available for the firewall software. I learned that the Kerio Personal Firewall software was acquired by Sunbelt Software. Sunbelt's rebranded version of the firewall doesn't run on Windows 98 according to Sunbelt's FAQ.
The Sunbelt Kerio Personal Firewall 4 requires 10 MB of disk space for installation and runs ONLY on desktop editions of Windows 2000 and XP. Kerio Personal Firewall 4 DOES NOT run on Windows 9x, Me, NT, 2000 Server and 2003 Server.Sunbelt doesn't support nor offer for download the old 2.1.5 version, which was available for free from Kerio Technologies, but states in the FAQ that it can still be found at various sites on the Net for download by doing a Google search for "Kerio 2.1.5" and that technical support for the older version can still be obtained from the Kerio Forum at CastleCops.