Foursquare. With it, you check-in to places (say a bar, restaurant, or even a park) using your phone, and it pings your friends who also have the app, and if you choose, pings your Twitter as well. You can leave tips for other people about the place, and if you check into a place more times than anybody else in a 2-month period, you become the mayor of that place. You can also win various badges, say if you check into a bunch of places with karaoke, you get a karaoke badge. It can be a neat way to let friends know you're out and doing stuff, or a way to coordinate for meeting up.
What's this mean for Columbia Heights folks? A number of businesses are using it, either to offer deals to people who check in, or to give specials to the mayor. I know Red Rocks, Tynan, Commonwealth, and the Heights have had deals: for example, Red Rocks and Commonwealth both give a free drink to the mayor. If you have the app and check in somewhere, if there are deals nearby, it'll tell you. So as well as fun, it might be a way to save some money or get some perks. Know of any other spots with Foursquare deals?