While social networks are great for connecting with friends online, they don’t provide a good way to connect with friends in real life. Facebook and Foursquare support check-ins that enable you to tell your friends where you are located, and they will show you where your friends who have checked in are located, but they don’t alert you if one of your friends are nearby. Banjo is a new app that attempts to provide just such an alerting service.

The idea behind Banjo is that you first connect the app with Twitter, Foursquare, Gowalla, and Facebook and then the app monitors those services in the background and provides a notification on your phone when a friend has checked in near your location. You can get the Banjo app for Android and iPhones, and I checked out the app on my Nexus S and iPod Touch.

Even before you connect it to a service Banjo will display a list of people near you who have posted on either of the social networks. In my test Banjo listed 16 people who posted within 4.6 miles of my location. Banjo lists the people near you in a grid of icons, a list, or on a map, and you have the ability to filter the display to only show your friends, or anyone near your location.

In order for Banjo to work best your friends either need to post a tweet with Twitter’s location feature enabled or check-in to Facebook, Foursquare, or Gowalla. For example, only a few of the people I follow on Twitter post tweets that include their location, so when I filter to only display friends I only see two, neither of who are near me.

If it happens that a lot of your friends on social networks live near you and they are comfortable with sharing their location, Banjo can be a useful tool for finding out when your friends are nearby. If you are like me and have your friends spread far and wide, or they don’t share their location then Banjo is not going to be very useful. Banjo is free, however, so if you are curious to check it out, you will find in the Android Market and the iTunes App Store.