M17 Protocol
M17 is a completely open-source digital voice protocol, designed for amateur radio use. Not a single part of it is patent encumbered. M17 uses Codec 2 voice codec.
Protocol’s specification is available through a GitHub repository.
There’s a list of supported radios, should you want to use Module17 or any other hardware with M17 support with analog FM rigs.
M17 Project’s website
M17 Project article on Wikipedia (available in 9 languages)
M17 Knowledge Base
WPSD Project
WPSD is a next-generation digital voice software suite & distribution for amateur radio use, enjoyed by many thousands of hams around the globe. It is used for personal hotspots and repeaters alike. It supports M17, DMR, D-Star, Yaesu System Fusion (YSF/C4FM), P25, NXDN digital voice modes & POCSAG data/paging.
WPSD is available as installable disk images, and multiple platforms & devices are supported. The WPSD Project is free and open-source software (FOSS), created and maintained by Chip, W0CHP.
WPSD Project’s website
WPSD Discord server
OpenRTX
OpenRTX is a free and open source alternative firmware for digital ham radios. The firmware is designed with a top-down approach with the objectives of modularity, flexibility and high performance. Currently, it is the only firmware with M17 support. OpenRTX is led by Silvano, IU2KWO.