The GeoBee Challenge iPad app from National Geographic is an excellent app that students can use to test and develop their knowledge of world geography. The contains more than 1300 questions about physical and political geography. Each round of the game presents the questions in a different manner. In some rounds students see a picture of a landmark and have to tap the country containing that landmark. In other rounds students read a question and tap the answer on the map. And there are rounds that simply present the name of a location that students have to locate on the map.
The GeoBee Challenge app is designed for elementary school and middle school students. Registration is not required in order to use the app and multiple students can use the same installation of the app. GeoBee Challenge is currently (March 3, 2014) available for free, but its regular price is $1.99.