Hydrogen
I have put considerable research into using hydrogen as a fuel to heat homes, cook food and power vehicles. It qualifies as an eco-fuel because it can be produced in a totally renewable way.
Alcohol
There are lots of types of alcohol, which are all eco-fuels. Alcohol is made from bio-mass, which is readily re-grown from the environment.
Wood
Wood is a standard bio-mass used for heat and power. Ships and trains used to be wood-driven, the wood being burned to create steam to drive the steam engines. Wood Gas is a way to use wood to power our 'modern' internal combustion engines.
Hydrogen Peroxide
During my research I've discovered that hydrogen peroxide has definite promise as a fuel of the future, particularly when combined with fuels that need oxidizing; like alcohol.
Turds
There are a couple of ways to use turds as fuel. First is to dry them and burn them like any other bio-mass. And second is to turn them into methane. Methane (also known as natural gas) is an eco-fuel made from bio-mass that can be used to power our 'modern' internal combustion engines.