My fitness pal, or MFP as some call it, is an app where you are able to track your daily activity as well as set calorie goals. I love this app for tracking calories because it already has several pre-entered foods. Calorie counting has never been so easy.
Myfitnesspal lets you add friends, set notifications so you can be reminded if you haven't logged in, and shows you in-depth charts of how many calories you've consumed and your weight loss.
I'm giving it 9/10 for its features. No it doesn't plan your fitness regimen or track every step you take, but you already have apps for that ("health" app on your iPhone).