OK, this one is only a good one if you run. I believe a cousin told me about it. Since I believe every blood relative I have runs, it does not surprise me.
It is an iPhone app. The basic app is free and the upgrade is $1.99.
What it does: Many things. It uses the GPS and can track / record your running routes. It times them; measures them; gives you average pace; miles per hour; elevation; and many many more things. It also measures calories burned and other fun health-related stuff. If you buy an attachment it will also monitor your heart rate and other vitals.
I find that it is motivating and sort of fun. Also, and I am still exploring this aspect, it can act in a similar fashion as Facebook in that you can make your runs public or private and have the option to create your own community - including finding other people to run with if you wish. There is also a companion app I believe for those who bike.
It is a little bit buggy at first and does take some adjusting but I find the effort worthwhile. See it at this link: