A free, open-source, multi-platform application for sending files and messages, using the codec2 HF modems.
Dire Wolf is a software "soundcard" AX.25 packet modem/TNC and APRS encoder/decoder. It can be used stand-alone to observe APRS traffic, as a tracker, digipeater, APRStt gateway, or Internet Gateway (IGate).
In the early days of Amateur Packet Radio, it was necessary to use an expensive "Terminal Node Controller" (TNC) with specialized hardware. You can now get better results at lower cost by connecting your radio to the sound card of a computer and using software to decode the signals.