So I play this game called Pocket Frogs, in which players collect and breed various color-combinations of frogs. It's a Mobage game -- Mobage makes freemium app games for iOS and Android. There's a pretty good play/cost balance, where you can get a lot out of the game without ever spending any money, but I really want to baby-proof another one of my habitats (you start with one nursery) so that I can breed more frogs at once. That costs 499 MobaCoin, or $4.97.[1. I would have some more MobaCoin left over after that transaction, but since they're sold in batch increments, that's the smallest amount of money I could pay to get a sufficient quantity of MobaCoin.] Instead of paying that, I'm just taking their pop-up offers, to download and start playing various other Mobage games in exchange for MobaCoins. I'm up to 175 through these promotions, and I've started spending a lot more time playing one of the games, Defender of Texel (D.O.T.)
In D.O.T., players control a three-by-three grid of fighters, with which they explore linear dungeons full of random encounters. Players have a high degree of control over the arrangement of their fighters, and reasonable control over their stats -- and during combat, choose the order of attacks, by drawing three tic-tac-toe style lines across the grid, forming three self-managing waves of attack against the enemy lineup.
There's also a semi-complicated system of evolution, to improve fighters, but I won't get into that. The point is, Mobage's business model appears to be successful. They have now enticed me into regularly playing two of their games, to the point where there's stuff I meant to have done by now today, that I haven't started on. Like getting dressed.