A few of the larger Swiss Army knives include a hoof cleaner (aka hoof pick). It's a curved, blunt blade that is perfect for scraping stones, mud or other crud out of your horse's hooves.
Uses: To use the tool, just pull it out of the knife body, hold it point forward, and scrape along the cracks and crevices at the bottom of the hoof, until you have removed all foreign materials.
NOTE: in an emergency, one could probably use some other blade or tool to remove a stone or mud. However, it would not work as well, and might cause injury. It is a shame that the Equestrian model was retired in 2013.