Retrica is a camera/selfie app that comes with loads of filters and collage layouts. It's an absolutely must-have for anyone into selfies. Its design is also pretty slick and poppy, with no added distractions to shift your focus away from the task at hand—taking a selfie.
Writeily is a minimalist markdown editor. It doesn't come with fancy animations or crazy add-ons, but it does its job well. Its beauty is utterly utilitarian.
Coursera is a nifty app for you to access college courses on your phone. Gone are the days of massive student debt and physical classes (just kidding; both are here to stay). I'm not kidding, though, when I say that the free lessons provided are myriad and interesting.