HestiaPi has a tiny computer inside it to do most of the work. It has a white on blue back-lit LCD display to show all the information needed and 4 buttons: Heating Boost, Hot water Boost, Increase Heating Temperature and Decrease Heating Temperature.
It can measure the room's temperature and react to it according to scheduled commands or manual boost. It can turn the heating or the hot water on independently.
It is connected to the Internet via WiFi. Wired Ethernet is also an option.
With its screen and buttons acts as a typical thermostat and no extra devices are needed to operate.
Being connected to WiFi though allows you to control it from your smart phone and use all of HestiaPi's features.
It runs on mains 110 - 240 VAC although an external 5V transformer could be used if required.
Its enclosure measures 17.5x8x2.5cm, that is roughly 7x3x1 inches.