[Someone]

> Sarajevo War Stove was a large 1-2l tin can, conducts heat directly and doesn't absorb much itself, lets you boil water or make some small soup.

Efficient stoves can indeed be fairly simple, as in https://en.wikipedia.org/wiki/Beverage-can_stove, https://en.wikipedia.org/wiki/Hobo_stove or https://en.wikipedia.org/wiki/Rocket_stove.

A hightech variant has a battery-operated fan. I find that a weird combination, but apparently, it works well (https://www.techxlab.org/solutions/zz-manufacturing-sierra-z...)