(There's no video for FAXstf 6.0 yet. Please contribute to MR and add a video now!)
FAXstf 6.0 is probably the best modem faxing application ever made for Macintosh.
FAXstf_6.sit (3.91 MiB / 4.1 MB)
FAXstf v6.0 installer / compressed w/ Stuffit
Requires a faxmodem, obviously.
Emulating this? It should run fine under: SheepShaver