An evaporative system provides cooling by drawing air across a series of wetted "pads". Water on the pads evaporates as the air flows over it, cooling and humidifying the air.
Evaporative systems are sometimes also referred to as a "swamp cooler".
Evaporative systems tend to use less energy than split or ducted systems, however, unlike split or ducted systems they consume water to provide cooling.
Note that because they rely on evaporation to function, evaporative systems can only be used in some parts of Australia - they are not appropriate in areas which experience high humidity (costal regions in Queensland, for example), as the air already has very high moisture content. Ask your licensed contractor if evaporative cooling is suitable for your area.
You will also need to make sure you leave some windows open to allow air to flow in and out of the house, otherwise it is possible for condensation to form inside the house as a result of the elevated indoor humidity.