Devices like smartphones and GPS receivers are enjoying unprecedented popularity in the consumer market. The Apple iPhone broke new ground in the smartphone consumer market and has established a new industry in smartphone applications. The combination of these factors has inspired dozens of developers to create innovative games and applications for handheld devices.

Dennis Crowley and Naveen Selvadurai are two such developers. Crowley has a history with Web applications -- he developed a mobile device service called Dodgeball. The idea behind Dodgeball was simple: First, you text your current location to the Dodgeball service. The service would then send that information to other Dodgeball members in the area. The idea was that you could use the service to meet up with old friends or make new ones while out on the town.

Google purchased the Dodgeball service in 2005, but eventually shut it down. Crowley didn't let the setback discourage him. Instead, he worked with Selvadurai to develop a new service called Foursquare. It bears some similarity to the earlier Dodgeball application but has its own set of features that make it unique.

Foursquare doesn't just broadcast your location to other users. It also serves as a game, pairing virtual rewards with real activities. Users earn badges as they visit different spots. Visit one location enough times and you become the mayor. You can use Foursquare to meet new friends, find out who else is in your area or compete against other people in your city.