Hylafax

"HylaFAX is an enterprise-class system for sending and receiving facsimiles as well as for sending alpha-numeric pages.

The software is designed around a client-server architecture. Fax modems may reside on a single machine on a network and clients can submit an outbound job from any other machine on the network. Client software is designed to be lightweight and easy to port. "

http://www.hylafax.org/content/Main_Page