I've built a few and it's kind of exciting when you get it right. (I live a dull life.) When you get everything right, the flame turns blue and it makes a tiny roaring sound.
They burn scraps, and the combustion is much more complete than a plain open fire.
There are a number of projects to supply gasification stoves to third world residents. Fuel for cooking and heating is a major expense for many people in the third word and gasification stoves can reduce fuel usage by 2/3! This is a huge boost in disposable income for them. It also has the potential to create a major reduction in CO[sub]2[/sub] emissions.