Tomodachi life is a game where you build an island of miis and see what they do.
You make them sing, you can feed them, you can give them different clothes and apartment rooms. Each mii has a personality you give it and this affects how they behave on the island.
I personally love this game, purely because it was the first ever 3DS game i played. Fun fact: in Japanese, Tomodachi means "friend".
Yeah, thus game is my friend. Love it!