Without.

The Without app has a rather sweet story behind it. You can read the whole thing here (which I recommend you do) but the gist is that developer Jeremy Schoenherr found himself in a long distance relationship and wanted a way to keep in touch with his lady without going through the traditional seemingly naggy routes. So, he made an app that allowed him to keep in quick contact without feeling like a heel.

Turns out, the concept works for people that are in relationships in the same town as well. So, he fleshed it out a bit and put it in the app store. Now anyone can try it out. I think the story behind it seems so pure and heartwarming, it's hard not to love.