E-85 Ethanol

What types of cars does this form of gas run in? And why can it not be used for the Geo metro? I know that E-85 will work but what is the difference between it and the one made with ethanol?

They're both ethanol, just in different amounts. Regular gas is now often 10% ethanol, called E-10 officially but usually not labelled as such so as not to confuse. It's a small enough percentage that any car can use it. E-85 is 85% ethanol and should only be run in cars designed for it, the car is usually labelled as "flex-fuel". Ethanol (and or) the water in it can corrode aluminium and some kinds of rubber seals and gaskets. Also ethanol has less energy in it than gas, so your performance and mileage will go down. Most of this loss can be regained with higher compression, advanced timing, and different mixture rates, but our cars aren't capable of making those adjustments.

E85 is bad on your standard fuel lines and aluminum in vehicles that are not flex fuel capable like Woodie said. Flex fuel vehicles typically run a lower compression ratio as E85 makes MORE power than regular gasoline. Dyno results have shown an increase in horsepower with E85 as it is around 100-105 octane versus gas at 87-93.
Using E85 in a vehicle with say a 9.5:1 or 10:1 compression ratio would make more power but a definite loss in MPG's.
My wife owns a 2005 Ford Explorer that's E85 compatable and we never run it in it anymore because we lost around 3 mpgs and when it only gets 17.5 to begin with it's not worth the 30 cent savings at the pump per gallon.