TomTato plants are available for commercial use in Britian and they are a single plant that grows both tomatoes and potatoes. Potatoes grow in the dirt and tomatoes on the vine. The plant was created by grafting the two plants together. Hybrids like this have been available for years but have been plagued by lack of taste, but the TomTato has overcome this problem.
The benefit to having the single plant is that it's possible for people without a yard to grow them in pots, so more people can be gardeners. The TomTato is good for one growing season and the potatoes are ready to harvest when the tomatoes have ripened.