Foursquare is awesome for meeting up with friends - it notifies you when a friend checks in close by so that you can go meet them. But, sometimes a friend checks in while you're busy - at dinner, seeing a movie, etc. You want to hang out with them when you're free, but you won't unless you put in a lot of effort into co-ordinating plans for later. That's where HangoutLater comes in. When you checkin somewhere, HangoutLater notifies you on Foursquare that one or more of your friends have checked in close by recently. It then suggests a fun place between all of you where you guys can meet up when you're free.