EWF redirects writes that would usually go to your hard drive to ram. By reducing the number of writes you can make solid state drives last longer.
HORN is used to make people get out of your way. Often it's the button in the middle of your steering wheel.
HORM on the other hand (which is what I suspect you wanted to ask) allows you to reboot from a single hibernate image multiple times. It allows a fast boot from a stable image with no requirement to hibernate on shutdown.