We have three baby apps that we use frequently.
The first one is a white noise app. My husband and I have different versions of the same thing, but they both work pretty effectively. Most of the time, Jacob will nap without issue, but if he is super fussy and doesn't want to nap, one of us can whip out our phone and play our white noise app to get him to drift off to sleep. We both got ours free on the iPhone app store.
The second one is LifeCake. This is an awesome photo library app that sets up a timeline of your baby photos. As long as the photo was taken on your device, it will arrange the photos in chronological order and display the baby's age on each photo. It even works backwards if you add your pregnancy belly photos! I have pictures of my positive pregnancy test on up to current pictures of Jacob!
A neat feature of the LifeCake app is that you can invite other people, so my husband and I have one account and we can both add photos and videos. You can also invite people to view the photos, so all of the grandparents have access on their devices as well. This is great because the grandparents can check and see if new photos have been added whenever they want, and my husband and I don't have to blitz people's Facebook timelines with a bazillion photos of Jacob all at once.
The third app is called BabyConnect. We had to pay for this one, but it has been awesome. In the hospital, the nurses gave us a chart to keep track of time spent breastfeeding and wet and dirty diapers. Being the data freaks that my husband and I are, we got home and started using BabyConnect instead. Any time you change a diaper, you can log it on the app. You can even note the size, color, and consistency of the poo. You can time naps and overnight sleeps. You can track how much time is spent breastfeeding or how many ounces of formula your baby gets. All of this data shows up on a daily timeline so you can see just how your baby spends his day.
Don't know if we still need to keep track of diapers, but BabyConnect helps us to know how many ounces Jacob has had, because if he's had a full belly all day, he usually sleeps really well at night!
Do you have any baby apps that you've found to be really helpful?