The ptFlex Flight Controller the second generation of Trackers from Project: Traveler.  It is an Atmel ATmega328p based microcontroller that functions as a stand-alone tracking system.  It can be easily integrated with other systems using SparkFun Electronics' Qwiic I2C connector.

The ptFlex is open source hardware and software, and can be built by yourself from scratch, by purchasing a kit of parts, or by purchasing an assembled kit from Custom Digital Services.