Panther introduced built-in Fax receiving, but has no mechanism for alerting the user that a Fax has arrived. Until they make one, here's an easy way of doing this by installing a folder action script.

Version 1.0 (Size: 92441 bytes) is for Mac OS X 10.3 (Panther) and up.

Fax Alert Installer is freeware. However, if you think it was useful to you, you may contribute with a donation.