Like cats? Want to collect a bunch of them without being the creepy cat lady down the street with the outrageous food bills?
Neko Atsume is a cat collecting game. The simplistic mechanics make it incredibly easy to pick up. You just set out food and a toy, turn off the app, and come back later to find cats playing, sleeping, or lounging around your yard. The cats will leave you gifts of fishes because they enjoy your yard so much, and you use the fishes to buy more goodies.
Neko Atsume is a free to play game, and occasionally they do update it with more goodies to buy and more cats. The ads are unobtrusive, and in game purchases are limited to little gold fishes which you use to buy some of the pricier items, but they also let you purchase gold fish with regular fish so it is possible to gather all of the cats without ever paying for anything, it just takes a little longer.
Neko Atsume seems to make its money in merchandise, rather than through the game itself. You can purchase your own stuffed kitty, figures, t-shirts and more with the adorable cats on it. The Neko Mart in Japan sells nothing but Neko related merchandise, and lots of it. But if you live in the US you can always purchase your favorite cats online. Check the wiki for a full list of available items.