Fax or Exchange "style" servers for OSX


Has anyone heard of any Fax servers which can act as gateways for OSX?

For instance, in M$ Exchange Server you can set up profiles for customers or business partners which when you send a message to the server will either email or fax according to the preference set for the receiver.

Are there any Unix (or OSX) based apps out there that can have multiple OS clients, and has the same functionality?

Please let me know at rholmes@mac.com

G4 Cube, 192MB RAM, 20GB, DELL Monitor (I borrowed it from a DELL guy who can't be bothered using his PC. :)
I found one.

Communigate Pro.

It runs on loads of platforms, and is very very well priced. http://www.stalker.com.

Now I've downloaded it, I need to find a machine I can test it on. Anyone have experience using it on other platforms?