Occasionally, we come across a technology that has just kind of been forgotten about. Take this Ural motorcycle. It runs on a substance called wood gas, which is the byproduct of incomplete combustion of carbon products like wood, hence it's name. The fuel goes through a process called gasification in a wood-gas generator to produce combustible hydrogen and carbon monoxide. So basically, you're burning wood to produce fuel.
Ural Patrol T and Red October - Click above for high-res image gallery
Ural T sidecar motorcycle - Click above for a high-res image gallery