FaxCenter is a small ANSI C/POSIX program that sends and receives faxes using almost any fax modem (internal or external).
Cocoa eFax started as a simple front end, but has really progressed into much more. You can send and receive faxes in multiple formats. You can scan and send, you can send quicknotes, attach coversheets, and much more.
What's new in FaxCenter
Fixed the issue where faxes were sent out inverted on Mac OS X 10.3 and earlier