Vgetty turns your voice modem into an answering machine. It adds voice capabilities to mgetty. This means, that you can handle data, fax and voice calls on one telephone line.
HylaFAX™ is an enterprise-class open-source system for sending and receiving facsimiles. This is the place where users can find HylaFAX+ support, work, and releases. The "+" means that it is better.
IAXmodem is a software modem written in C that uses an IAX channel (commonly provided by an Asterisk PBX system) instead of a traditional phone line and uses a DSP library instead of DSP hardware chipsets.