Ebay, self powered Peltier stove fan in operation.

This fan is used to circulate warm air from a solid fuel stove around the room. It sits on top of the stove and is powered by the heat differential between the thin base section in contact with the stove-top, and the larger area heatsink above it, that is cooled by the fan when it runs.
The power for the fan is generated by a very common peltier module often used in car-fridges, but actually being used to generate power in this application. Basically speaking, if one side is hotter than the other it will generate a small amount of electricity.

Don't be tempted to make your own, since these are pretty much engineered to perfection with custom aluminium extrusions. They look stylish and are much cheaper now than they used to be. They also have some specialist features like a bi-metallic strip on the base that physically tilts the fan back if it's getting too hot, to reduce it's area of contact with the stove.

You can find these on ebay if you search for stove fan. But make sure you shop about, as the same fans are being sold for wildly different prices. In the UK £40 inclusive is typical.

When the stove is lit the fan will not run until the temperature is high enough, and will then often ramp its speed slowly up and down until it reaches a point where the heat of the stove and the fan cooling of its heatsink reaches an equilibrium.