Facebook has unveiled Facebook Places, which is its entry into the social location market previously epitomised by Foursquare. In short, Facebook Places lets people check in to real-world locations, and tag the friends that they’re with – albeit with privacy controls to ensure nobody gets tagged who doesn’t want to be. Developers can build mobile apps on top of the Facebook Places API too, which gives scope for apps based around live music, for example. Foursquare, Gowalla and Booyah are all signed up to use the API already. For now, Facebook Places only works in the US though.