Slope is a little utility to convert the steepness of a road expressed in degrees to the slope percentage you have probably found on some road signs while driving in your car. It can convert in both directions.
Obviously you can do the same thing with a pocket scientific calculator, but with Slope you can also see a simple graphical representation of the road with a car on it, and have a better feel of what a certain inclination actually means!
If you have an off-road car maybe you will find this amusing :)
|Slope running on XP||The equivalent road sign|