What is the US equivalent of a Toyota Aygo?

There isn't a direct US equivalent to the Toyota Aygo. The Aygo is a very small, city-focused car, and that segment isn't as popular in the US market. Cars like the Smart ForTwo are closer in size, but even those haven't achieved widespread success. The closest comparison might be some of the smaller trims of cars like the Toyota Yaris (though the Yaris is slightly larger) or the Hyundai Accent, but even these are notably bigger than the Aygo.