In the age of the smart home, we need standards not just for the devices themselves, but for the glue that holds those devices together. There are so many different ways that electronic devices can communicate -- WiFi, Bluetooth, and newer protocols like Z-Wave -- that a world in which it's crucial that one device be able to talk to another could quickly turn into a Tower of Babel if those devices are speaking different languages.
The Venstar T3900 Voyager smart thermostat was designed with the understanding that it might be needed in a number of different environments. To make it compatible with those environments, the designers have made it capable of communicating via the WiFi, ZigBee or Z-Wave protocols. You're almost certainly familiar with the first of those protocols, but the others are less familiar. ZigBee is a simpler, and therefore less expensive, alternative to WiFi and Bluetooth. Z-Wave is a system released in 2005 specifically to monitor full-home automation.
A smart thermostat like the Voyager could obviously be a central component of a self-running home or even a self-running office, so giving it this many ways to communicate with other devices could be crucial to the way we live in the very near future. Voyager is actually a line of seven different thermostats, some for residential use, some for commercial use, even one for use in schools. With that many different models, it's not surprising that the thermostats need to understand multiple languages.
The Voyagers not only control temperature but also humidity. And they can be operated not only from iOS phones and Androids but from Blackberries. Clearly the Venstar Voyagers are intended as an industrial strength system for environments both large and small.
Should you need something less ambitious, however, you may be better off going with a less powerful system designed strictly for home use, like the smart thermostat that started it all, the Nest Learning Thermostat.
Model T3900 is dual-fuel capable, with controls for humidification/dehumidification and the option to lock out auxiliary heat based on outdoor temperature.