Popular examples include Doubledown Casino, Slotomania, Zynga Poker and myVegas Slots. Social casino games differ from real-money gambling by several distinct features. First, social casino games do not require monetary payment to play, rather players' wager virtual credits.
The fact that you do not use your money to wager is simply the main reason social and sweeps casinos aren't considered gambling sites. Social casinos and online Sweepstakes have recently become a craze in the United States and are legal in all but 3 states.