According to Wikipedia, a Rocket Stove is:

an efficient cooking stove using small diameter wood fuel which is burned in a simple high-temperature combustion chamber containing a vertical chimney and a secondary air supply which ensures almost complete combustion prior to the flames reaching the cooking surface.

Last night I was fortunate enough to have drive of one that Rob and Ken had knocked up during the week. The ingredients were:

and the result was this:

Rocket Stove

Ignore the larger sticks in the picture above, this rocket stove generated an awful lot of heat using little more than bark and kindling while the kitty litter kept the outside cool enough to touch. It was brilliant.

A rocket stove generates high heat and very little smoke, keeping the air as clean as possible. You can even make them with as little as 16 bricks. There are 6 plans here which are very simple and easy to do.

As it turns out, there are a lot of possible uses for these little beauties.