Health and fitness applications are a major category on smartphone app stores, representing about 20% of available apps. These apps cater to a wide range of users, including doctors, patients, athletes, and anyone concerned with their health. They offer specialized tools for areas like sleep tracking, exercise, and social networking for health communities. The iPhone is a good platform for health apps due to its large app store, connectivity, and sensors that support features like GPS and activity tracking. Examples given are Sleep Cycle alarm clock and Nike+ GPS.