The bio-gas digester is a great low-tech solution for the need for cooking fuel in developing (and why not developed?) countries. It collects waste from livestock and people, harvests the gas for cooking, lighting and/or heating, and produces organic fertilizer for crops. Using bio-gas instead of wood or charcoal greatly reduces smoke inhalation and related diseases (especially in women who do most of the cooking), deforestation, carbon output, time spent gathering firewood or money spent to buy wood or charcoal. Different types exist, but this is an illustration of the basic concept.