Today I have publicly released the TETRA receiver code that I've started to work on earlier this year. The gnuradio-based demodulator, PHY and lower MAC code as well as some README file is available from the new http://tetra.osmocom.org/ website.
There's still a lot of work to be done, but fundamentally we are able to receive, demodulate and decode TETRA TMO downlink data. So the task of the software somewhat compares to that of gsm-tvoid or gsm-receiver (part of airprobe).
A corresponding project mailing list has also been made available. Please respect that this is a development-only discussion list right now. If you cannot make the code work and need help with it, chances are high that it doesn't do anything useful for you anyway.
There is some early code that should eventually enable us to run a base-station side transmit implementation, but it's not working yet.