“In the aftermath of a disaster, purifying drinking water may be a priority. The quickest, safest method could be boiling. This biomass stove only requires four concrete blocks, a tin can with both ends cut out and a gas stove eyelet top. The completed stove is sturdy enough to hold a several-gallon container of water, stew or a heavy cast iron Dutch oven.”
The free online document linked below has several interesting low tech/low cost stove designs from around the world, including some commercial scale stoves for feeding lots of people.