aprx was originally a receive-only APRS iGate software, now extended to do 
digipeating, and Tx-iGate. It works on any UNIX-like systems with minimal 
requirements of system services, or system libraries beyond basic POSIX libc.

The software is to be installed on a suitable UNIX-like system, and its 
configuration file is then to be adjusted. Then it can:
* Handle arbitrary number of radio modems connected to itself
* Optionally relay APRS packets from radio receivers to APRS-IS 
  (http://www.aprs-is.net) network
* Optionally digipeat AX.25 packets with and without APRS NEWn-N 
  paradigm rules
* Optionally relay APRS packets from APRS-IS network to radio channel 
  (Tx-iGate)

This software is intended for very limited resources environment, like small 
embedded-like machines barely able to run the operating system with TCP/IP 
networking.
A receive-only Rx-iGate does not need any sort of licenses in most parts of 
the world where radio amateur hobby is permitted to begin with.

On version 2, aprx has gotten the ability to do APRS Digipeater function, 
Aprx Tx-iGate, as well as a variation of that called Viscous APRS Digipeater, 
which is an excellent choice for a Fill-In digipeater like on a mobile 
station. Viscousness means that it will listen for other copies of same 
packet for a small configurable number of seconds, and if it hears same 
packet only once, it will do normal digipeating for it.

aprx can optionall be used with soundmodem in place of a hardware TNC.