The San Francisco Marathon app allows you to track the progress of a friend or family member running the race, from your computer, iPad or smartphone. The app locates runners by using radio transmitters that come with their numbered bibs. It's made by MapMyFitness.
"So if you are like on the route, you can see your location and the runner's location," explained Scott Laing of MapMyFitness. "So you can kind of tell when they are coming around the bend so you can get your signs up, get your horns out and really cheer on your friends.
MapMyFitness is working on a new feature that would allow you to actually send messages to your runner during a race.