Those are merely the most convenient method to keep the car you own running.
You're free to build a wood gassification rig and modify the engine to run on that. You're free to modify it to run on high-proof alcohol and refine your own. In theory, you could strike oil on your own property and refine it in small scale to make your own gasoline. All options inconvenient and expensive, but possibly legal with certain safety and environmental restrictions to contend with.
You're probably not free (due to DMCA reverse engineering restrictions) to modify your Revolv to build your own version of their server architecture.
Let's agree to keep it simple.
Best Answer: Diesel. Runs on almost any fuel oil including vegetable oil, although petroleum-based fuel oils are easy to refine; it's definitely DIY-able if need be.
Next Best Answer: Alcohol would be the gasoline-powered alternative fuel, requires a doubling of the fuel:air ratio but that's it.
No need to go any more exotic than the above two, which cover