Well, providing you have an iphone/ipod that is.
It's called 'Zombies! Run' and is an interactive game in where you have the app ticking away in the background as you run/jog/walk listening to your music. It kicks in at regular intervals with instructions and Zombies chasing you - pushing you to go that little bit further. Makes a dull run or walk loads more interesting.
I'm probably not explaining it very well - but check it out.
Just thought I'd share : )