The ax25-apps package contains programs for the hamradio protocol AX.25 that would be used by normal users (as opposed to network daemons). While not essential, these programs are usually installed if you want to connect to amatuer packet radio networks. Generally it is a good idea to also get the ax25-tools package so you can configure the hamradio ports. This package includes call, listen, ax25ipd and ax25rtd.
