We've had our fun with Zombies, Run! before. The fitness program/zombie horde simulator is one of the more innovative ways we've seen to get in shape. However, it's not all casual fun. Sometimes you have to get serious. If you're looking for an app to push you a bit harder, you may want to check out Zombies, Run! 5K Training. Currently on sale for $0.99 in the Play Store (75% off), this one gives you more in-depth structure to get you through a full 5K in 8-weeks.
The app should work much like the regular version, with audio stories to augment your running experience.