Well, you learn something new every day. Today I went to a demonstration of a rocket stove which has been designed for "non-developed or less-developed nations in Africa, Asia, Latin America, or the Middle East" according to the not-for-profit company that retails them. The site explains, the "original Rocket Stove was developed by Dr. Larry Winiarski and Aprovecho Research Center to address life-threatening cook fire smoke produced by the half of humanity that cooks by open fire to stay alive. This is a critical and global issue, exacerbated by a scarcity of fuel, increasing deforestation and pollution."
Anyway the one I saw this evening was built entirely out of recycled materials and costs nothing to make and nothing to run. It uses a few strips of cardboard and a handful of twigs for fuel, enough to boil a billy and toast all the slices from a loaf of bread.