There is only one that I know of: Globalfax 2.6.9 Even so, you must set Energy Saver to System sleep = NEVER if you are to receive unattended faxes from "sleep". The 2.6.9 update of 2.6.5 was designed to work with G4s, which it does quite well, but it is not officially "supported" for use on G4s. FaxSTF (6.0.5) is a basket case on G4s and 9.1. FaxElite looks pretty good in many respects but I was unable to get the demo to receive from even partial sleep. Both
FaxSTF and FaxElite hog the modem, requiring manual switching to use the modem for other applications. GlobalFax can be set to share the modem, or use it exclusively. Problem is that finding this software may prove difficult, since the new owners (Zoom) do not plan to continue with this stand alone software but will be continuing with versions for use with their modems. You need to have 2.6.5 (w/serial number) and the 2.6.9 update file and be willing to do without suport. But if you NEED to receive unattended faxes on your G4, there are no other options.