It’s quite interesting to see what movements there are in the open source community around Digital Mobile Radio or DMR in short. Jonathan Naylor G4KLX has been promoting an open source GFSK/GMSK modem project called MMDVM, short for Multi-Mode Digital Voice Modem, capable of tranceiving DMR, D-Star and Yaesu System Fusion frames. MMDVM runs on top of an Arduino Due or a Teensy 3.1 development board. A mirror of the MMDVM protocol specification is available here. If you like to get involved in the MMDVM project, join the MMDVM Yahoo! group. The group targets early testers and MMDVM developers. Mind that you have to have a valid HAM radio license to play with the transmitter.
Guus van Dooren PE1PLM has been developing shields for the Arduino embedded micro processor boards and has made an AMBE30000 available for testing. This inspired me to start developing a multi purpose, portable C library for dealing with the DMR protocol. The AMBE3000 shield implements the G4KLX MMDVM protocol. You can track development on our dmrlib Github page.
As of today there is full receive support, as well support for talking to the BrandMeister DMR repeater master(s). However, the project is nowhere near a public release yet.