YAAC (Yet Another APRS Client) is an application for accessing the Automatic Packet Reporting System (APRS) amateur packet radio network invented by Bob Bruninga, WB4APR. YAAC functions as an end-node and digipeater for APRS datagrams when connected to an AX.25 Terminal-Node Controller (TNC) and radio transceiver. With YAAC, you can:
In receive-only mode, anyone can use YAAC. To transmit information over the APRS network, you must be a licensed amateur radio operator with privileges to transmit digital data in your country of residence.
For more information about APRS in general, visit Bob Bruninga's authoritative website on the topic.
You can also view the original YAAC website.
Wiki: Building and Modifying YAAC
Wiki: Downloading YAAC
Wiki: Running YAAC