Encouraging you to "check in" wherever you are, Foursquare is a mix between a social network, a game and a coupon app. Prospective locations run the gamut from restaurants and bars to parks, offices and sports stadiums. Checking in can sometimes unlock special offers on merchandise, as well as virtual badges for bragging rights. Plus, the Recommendations feature can show you cool new places to visit. Other features include a home-screen Live Tile that displays friends' updates and a slick side-scrolling interface.