Sometimes an app idea can seem ridiculous, but after trying it, you feel compelled to use it again later. Then again. Then the next thing you know it is one of your top apps. Foursquare is a location game. You “check in” at a restaurant, park, airport or wherever and get points for your check-ins. You link up with friends and compete against them to see who gets around more. You can also share notes, tips and pictures of places with friends and the whole world. It goes without saying that this isn’t for someone concerned about privacy. With the right group of friends, you can have fun and discover new places.