This is awesome! I love this kind of stuff! Can't wait to try it out.
Quite easy to try! You will need the board ETH-RLY02 to try out. It can be bought quite easily anywhere in the world including through my company Aliatron. In North America you can buy through Devantech. There is also an 8 relays board ETH-RLY16 (newer version is called ETH008) that you can use for controlling up to eight electric devices.
This may be a daft question but what can you do with that relay?
Not daft at all. Quite legitimate question. In my example I am controlling two equipment in my Lab. You can say switch on Air Conditioner or open Curtains. With the board ETH-RLY02 you can switch ON or OFF two electric devices independently.