Zone controllers act as the brains in a multi-zone HVAC (heating, ventilation and air conditioning) system. The zone controller acts as a hub between the thermostats, HVAC system and dampers to direct airflow only where it is needed. As each thermostat calls for temperature change, the zone controller turns on the HVAC system and open the dampers to that zone.
A properly designed system will save energy, and in turn, money, as it causes the system to run less often, and individual rooms are conditioned much more qucikly when they receive more airflow.
These zone controllers from RCS are available in 2-and 4-zone versions.