Local developers are preparing to launch TriOut, an iPhone app that is kind of a merger of other popular social networking services like Twitter, Yelp and Foursquare -- but all locally for the Triangle.

The idea is that users will check in when they go to area businesses, updating their friends on their whereabouts. They can also post reviews, photos and other things that may be useful to other TriOut users.

TriOut has been an invitation-only app so far, with about 200 people testing out the system. It will become available to the public tomorrow evening through the Apple app store after a launch party in Research Triangle Park.

At the moment, the app only covers North Carolina and most of the activity is based in the Triangle area, from Pittsboro to Johnston County.