fax4CUPS is a very simple shell script that acts as a CUPS backend for a serial fax modem. Essentially, you print with lpr and the fax is sent. The nice thing is that you have CUPS around, and this means, for instance, that you can check whether your fax has been sent just using your favorite browser (as you would do for any other printer), even if the fax modem is really on a remote server. It supports efax, HylaFAX, mgetty-fax, and Capisuite.
TkScanFax is a TCL/Tk GUI fax program in ANSI C/POSIX with support for efax and multiple languages. It helps make the cover page, convert text files, PostScript files, and image files into fax files, and send faxes. It also uses scanners by using backends such as SANE. The efax program supports Class-1 faxmodems.
YaaCs (Yet Another Advanced Cati system) is written in Tcl/Tk to manage and realize computer assisted telephone interviewing (CATI) and telemarketing. It make easy monitoring survey progress (giving several information), and it allows the management of the the survey with several administration tools. It simplifies the interviewer's work reading all contact's data from an easy and functional GUI. It can send faxes via hylaFAX and save all contact's data in a PostgreSQL database.
TKFaxSpool is a frontend for mgetty's "faxspool/faxq/faxrm" send FAX programs. It allows you to send facsimiles and manipulate the fax queue, maintain an Address Book of FAX recipients, and view PostScript attachments using GV. It has a special commandline argument for lpd-style FAX-printer spooling so any program with a print button can FAX the print output, and also allows you to view incoming FAX/Voice messages by quick launch button for TKVOICE.