Requires an Arduino, 2x DS18B20 temperature sensors, and something the ardunio can trigger for chill and heat cycles. For two SSBrewtech fermenters (brew bucket, unitank, etc) that would be 2 pumps, power supply(s), and a 4 channel relay (or SSR).
Controllable either through the Arduino IDE serial port, USB connected to a Raspberry PI that is running the brewery frontend, or your own serial implementation.