Matt came across this on youtube the other day. A type of rocket stove I think. It would be very cheap to make and operate.

A sawdust burning stove which burns smokeless, unattended for over 8 hours per charge. Perfect for a woodworking shop or other small space.

I did a little more research and found a great article on Mother Earth News on building sawdust stoves. Here is the link to the article.

Alice found this one. These are designed and made by Kisangani Smith Group in Tanzania. They have a sustainable forestry and teach youth blacksmithing skills.