The benchtop microwave is the microwave of choice for nearly every household. Despite its name they can still be housed as a freestanding unit within a cavity of cabinetry or behind a door. They are cheap to purchase and with a standard wall plug do not need an electrician to hardwire.
The steam microwave is like the combination steam oven, but instead of having a convection heating element it uses microwave energy. Both steam and microwave features can be used independently or simultaneously. Steam microwaves can achieve more moist and nutrient rich food.
A combination microwave is an appliance that has convection cooking as well as microwave capabilities. These are almost always in compact 45cm tall units as they are designed to be a complimentary appliance to a single oven. They are unsuitable as a primary oven as the microwave is out of service when using the oven and vice versa. The combination microwave should therefore be viewed primarily as your built-in microwave appliance, with a bonus secondary oven at your disposal. At time of writing they are only readily available in a single, built-in format.
This microwave is very similar to a combination microwave but differs in that it is not designed to be switched between microwave and oven mode. Instead it uses the convection heating simultaneously with the microwave process. This results in products not getting soggy, like pizzas or pies tend to do in benchtop microwaves. It can even be used for grilling cheese or baking cakes.
A standard microwave set to 50% power operates by fluctuating between 100% power and 0% power on and off. An inverter microwave has technology that allows the microwave to truly operate at 50% power (or 75%, 90%, etc.). This regulation of energy allows for more even cooking and defrosting and is much more energy efficient. Inverter is a technology not a product, therefore can be found in benchtop, convection and steam microwaves.