Didn't see a topic about Nintendo's first smartphone app yet.
https://miitomo.com/en/
I originally just signed up for the point bonuses for the new Nintendo rewards program, but I've been pleasantly surprised. It's got the usual "Acquire and spend digital currency to dress up your avatar" stuff going on, but the Q&A aspect which is shared among friends is kind of fun, as is the "Miifoto" feature. Here's my failed attempt to land a marketing job with Nintendo:
There's some odd quirks in how you can only add friends in person or via a linked Facebook/Twitter account. (You'd think it would allow for direct adding by NNID or through Miiverse, but nope.)
I'm curious to see if they expand the app in the future: I get a vague feeling we'll see some Animal Crosssing-esque furniture/room customization, and personally I think it would be neat if they added integration with the Badge Arcade.