The late twentieth-century saw an explosion of computer applications. The early twenty-first century brings hundreds of thousands of smartphone sensors built into the smartphone as well as its portability and programmability have made it a device with almost limitless applications. Beyond the tons of games and productivity apps available, health and fitness apps track the miles you've run, the calories you've consumed and even your current heart rate. Internet radio and podcasting apps put you in touch with whole new worlds of audio. Compass apps, leveling apps and flashlights provide handheld utilities. Apps that let you paint, modify photos or create music tap into your creativity.