The Tracker2 was developed by N1VG, Scott Miller at Argent Data Systems. It is a feature rich TNC that includes bi-directional APRS tracking, KISS TNC, Digipeater, Weather Station support and more. Hardware and Software is open source and is constantly being updated.
There is a Yahoo Group where extensive information is available in the archives and files sections.
The Tracker2 is available for purchase at The Argent Data Store.