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Our smart phones can be efficient allies in our quest to live healthier lives, but they can also sometimes feel a little bit like beeping, chiming babysitters: There's my phone telling me to work out; there it is letting me know I'm late for my meeting, and, ugh, there it is making me feel guilty for consuming 747 more calories today than I should I have.

So imagine my delight when we discovered a free app for caffeine addicts that's less of a monitor, and more of an enabler—in a fun, functional way. With Caffeine Zone 2 Lite, you input the size of your beverage, the time you drank it, and how fast you sipped it. The simple-looking app, which was designed by two Penn State University professors (a cognitive scientist and a computer scientist), uses predictive modeling to figure out how much caffeine your body has absorbed and how much more you need to remain in your optimal alertness zone. You can also fill in details like your weight and bedtime to find out when the effects will wear off, when another cup will push you into the jitter zone, and whether that afternoon espresso will be likely to keep you up all night. You can even set alarms that will suggest when you need another dose. One of the app's designers told BusinessWeek that they hadn't received any funding from coffee- or soda-makers (although they wouldn't turn it down), so for now, he's just helping the caffeine-lovers of the world find their perfect happy place, one cup at a time.

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