SlackBuildsOrg/network/efax-gtk

It is a GTK+ front end for the efax program who can be used to send and
receive faxes with a fax modem, and to view, print and manage faxes received.
It also has a socket interface to provide a "virtual printer" for sending
faxes from word processors and similar programs, and can automatically
e-mail a received fax to a designated user, and automatically print a
received fax. It is specially nice for a single user's use, as probably he/she
doesn't usually need a fax server (i.e. hylafax).

See /usr/doc/efax-gtk-3.0.18/README.SLACKWARE for configuration notes.

Efax-gtk requires: libsigc++ (available on SlackBuilds.org)