What other apps do you use to stay fit?

So far I use Zombies, Run! as well. I plan on getting an Jawbone UP3 to track HR better, though it's new so I'm not 100% sure on if it links in any way.

Body Fat Log. It is simple but it tracks my weight and body fat level over time.

Strava

I use MFP, StrongLifts 5x5, RunKeeper, 10k free, and Zombies, Run! 3. During my runs I have all 3 of those last apps running at once!

For running I had been using Digifit iCardio as it paired with my old HRM, but since getting the new HRM I have been shopping for a new one and am currently using Endomondo (loving it currently and will probably stick with it).

For bodyweight resistance training I use the You Are Your Own Gym app.

For yoga/stretching I use Sworkit.

For calorie counting I use MFP...but to be fair I don't use the food logging currenyly. I still measure but keep each meal under the calories needed per meal to be on target for the day. I pretty much use MFP nowadays for the social aspect, and because it is the nexus point where all of my exercises wind up logged in terms of calorie burn, regardless of app used to track that workout. I imagine some point in the summer I will switch from maintaining weight to build muscles and strength to more of a cutting type regimen and that food diary will be used again.