MMDVM stands for Multi Mode Digital Voice Modem. There are alternatives on the market and some run as much as $200, but the Jumbo Spot I found costs $85 shipped from California.

What is Mmdvm?

MMDVM is an open source software project licensed under GPL v2, but with a note to say that it is intended for amateur and educational use only, with commercial use strictly forbidden.

What is Pi star used for?

The design concept [of Pi-Star] is simple: provide the complex services and configuration for Digital Voice on Amateur radio in a way that makes it easily accessible to anyone just starting out, but make it configurable enough to be interesting for those of us who can’t help but tinker.