The Multi Protocol Packet forwarder sources have been available at github for some time now, after months of testing on multiple platforms (RPi with iC880a, MultiTech Conduit and Linux workstation with MultiTech mCard and some testing on Kerlink gateways) the software can be considered stable and is promoted to release status.
The sources are available at https://github.com/kersing/packet_forwarder
For use on RPi platforms I recommend using JP Meijers resin build: https://github.com/jpmeijers/ttn-resin-gateway-rpi