Runtastic is a workout tracking program for Android. It lets you keep track of where you have gone on your run, bike ride, or walk (or a bunch of other means of locomotion) and using the GPS in the phone makes some estimate of how far you've gone and how much effort you have expended.
I've also used Cardiotrainer for this purpose, which has a similar reason for being.
It's really handy to have your device track where you go so that you get a nice map of your journey. Those trips where you're trying to find your way through an unfamiliar neighborhood generate a trail of breadcrumbs you can follow, and it's really helpful to have a good sense for how far away a mile is while walking. (For me, it's a mile to the Michigan Union.)
Both Runtastic and Cardiotrainer have a synthesized voice to give you details of your progress as you go. Runtastic is rather more sparing in its narration, which I find just fine. Both systems allow you to log your progress to a variety of online media like Facebook.
I started out using Cardiotrainer, and it wanted me to log a trip every day and keep track of myself. When I used to wear a pedometer, that was really easy to do, and I could type in a few numbers every few days and feel like I was keeping up with myself. It doesn't make sense to have any of these running all the time, and so I was fine with Runtastic keeping that detail in the background for me rather than the foreground.
Runtastic also has a feature, as of yet incompletely tested, that lets you know where your friends are right now on the map. That's actually the feature I want more than any to test out, because it points to the possibility that you could use this for something even a little more like a real time channel for careful coordination of where people are and what they're doing. I'm imagining getting lost and having this be helpful.
Both apps are free, and both have Pro or Paid versions that unlock a few more features.