ReWire

I've been on the lookout for a good meditation app for awhile. I'd used one or two that were basically just dressed up timers and was looking for something more.
I stumbled upon an app called ReWire that was getting rave reviews. It was designed to help you meditate by providing feed back. The process is that you pick some music to listen to during meditation and the app will randomly pause the music. When the music pauses, you tap the screen. If you don't the phone vibrates. If you touch the phone when the music isn't paused, the phone vibrates. The theory is that by focusing on the music and noticing the absence, you build concentration and mindfulness. It is based on real teachings.
The app also has a game/tracking element. You get points for every session. You are awarded points based on duration and accuracy. If you want, you can also hook ReWire to Facebook and see how rank amongst other users.
Ultimately, the app didn't work for me. It does what it says on the tin and does it well. For me, the way it worked was the issue. I found it distracting to always be tapping the screen and the pauses in the music were grating. I also found that if you used music with any quiet sections or natural gaps, it was hard to decide when to tap the screen. I never bothered with the social aspect, so I cannot really comment on how that helps or hurts the app.
For me, the simple timer apps work the best. They ding at the beginning and at the end. The rest of the time, they get out of the way and let you do your practice. Less is best.