Score is a high efficiency woodstove that uses about half
the wood (or dung) of a regular wood fire, creates an even smaller
fraction of the smoke (a health hazard with regular fires indoors) and
uses the waste heat of the stove to power a thermoacoustic generator
to create electric power to power some LEDs and/or charge
cellphone batteries. Later versions will power a computer

Aside from the obvious fuel saving and health advantages to the users
of the stove, the efficiency of the device reduces the amount of
carbon that ends up in the atmosphere. Some estimates place the impact
of wood cooking stoves at close to 18% of the total greenhouse gasses,
creating 800,000 metric tons of soot worldwide a year. With half of
the worlds population using wood stoves to cook and nearly half the
wood in the world being used for cooking, this stove (and similar
devices) could change the world.

The thermoacoustic innovation is a big bonus because it's cheap, very
reliable (one moving part) and uses heat that was going to be wasted
up the smokestack. It works by exploiting the fact that a properly
dimensioned tube that is heated at one end and has a porous heat
absorbing substance (steel wool...) separating it from the cooler end
of the tube will generate a sound (Google thermoacoustics). If you
attach a loudspeaker to the open end of the tube the sound will
oscillate the coil in the speaker and that moving coil will generate
electricity (this is how microphones work). The refrigeration part is
a little trickier. If you take the same tube and drive a sound into
it, the air moving past the heat absorber, the air compressing (and
heating) and decompressing (and cooling) will cause one end of the
tube to get hot and the other to get cold. So if you combine two of
these devices, with one using heat to generate sound and the other
using the sound to pump heat out of a small fridge with a modified
loudspeaker/generator between the two, you have an extraordinarily
clever and useful device.

All of this for only £20, ($40)!
 

Explanation courtesy of  Michael Crumpton, http://artformfunction.com/