My friend Paul (@Crazyblazerfan) follows me (@netback, @layPhone, @mmtank) on Twitter and finally asked me the other day what in the world Foursquare was and why I always have tweets about it. Foursquare is a social check-in service which lets you and your friends let each other know what you are up to and where you are at. They recently reached the 10 million user mark (I was #506,620) and continues to grow.
Basically you open the app on your iPhone (or almost any smartphone) and it looks for locations near you. It will pull up businesses, parks or just about anything that is into their database. It will also let you add places that don’t show up, like I did for my house. Once you find the place you are you can add a quick note about what you are doing, a picture or a tip for other people who might visit in the future. Then you hit check-in.
Now here is the fun part. You get points for each check-in. The basic check-in is 1 pt. and I think I have gotten up to 9 pts. for a single check-in. It is based on whether you have been there before, if your friends have been there, etc. You can also become the mayor of a place if you visit there often. There are also badges that you unlock for various adventures. They also have an explore section to find places around you that people have visited.
It is a fun little service that I definitely enjoy using. It is interesting to see what my friends are up to or if any one else has checked in where I am at. I have mine connected to Twitter but when I am checking in it is very easy to not tweet it or not even share it with friends if you just want the points (think gas station).
foursquare [free] 
