Having a washer and dryer in the home is way more convenient than lugging your clothes to the nearest Laundromat, but the combination can have some downsides, too. Like when the two machines are hulking masses of metal and take up an entire wall.
When real estate is tight, architects build up. You can, too. Stacking your dryer on top of the washer lets you take advantage of unused vertical space. Single-unit stacked washer-dryers range from small capacity to full-sized, Energy Star qualified, front-loading versions that cut down on water and electricity usage.
Stackables are sold as separate units, and you'll probably need a stacking kit to hold them together securely. But just think of what you can put where the dryer used to sit. It's like adding a new closet!