It's such a good app~! :D
Try it out; Nintendo made it themselves!

Available on iOS and Androids by the way! >w<
Not all phones/ tablets are compatible though.

If you own an iPhone, it should be past iOS 7.1 for the app to be able to install.

On Miitomo, I made the Mii look exactly like the one on my 3DS >w<

Have fun~!