A toaster will do exactly what its name suggests: toast bread. These simple gadgets have evolved, however, and you can use them to toast or thaw different frozen baked goods. There are also models that offer large capacities which will let you toast 4 to 8 slices of bread at the same time. However, they are still much simpler than toaster ovens, since their main function is simply making perfect toast every time.
Toaster ovens, on the other hand, are bigger gadgets that have the functionalities of both toasters and traditional ovens. You can still make toast in these ovens, but you can also bake, broil, and cook a huge variety of meals. Thus, they tend to have a larger number of features than simple toasters.