Solar ovens are popular with boondockers in sunny areas because they require no power to operate. All they take is sun and time (both of which the boondocker has in abundance.)
A folding oven is a stamped metal box that folds flat for storage and unfolds into a box for stovetop baking. The most famous example is the Coleman folding oven.
Most types have a built-in thermometer and rely on stove output to regulate temperature. Because of their small size and light weight it can be difficult to keep an even temperature; lower flames are easiest to adjust.