If you buy a car today, it will probably come with some kind of touchscreen computer onboard. These are basically embedded tablet computers that run some kind of operating system, but rather than coming from Apple, Google, or Microsoft, the software comes from car manufacturers and their suppliers. Car companies don't have a ton of experience when it comes to software, so the integrated computers generally aren't designed very well. They also never have the app ecosystem we've come to expect from smartphones and tablets, so it's no surprise that many people still prefer using their smartphones over the in-car option.
Traditional software companies are getting a foothold in cars, though. We already reviewed Android Auto, and recently we got to spend some time with Apple's CarPlay. CarPlay seeks to combine the benefits of the in-car system—namely the big, bright touchscreen—with the design, apps, and functionality of iOS. Plug an iPhone into a supported vehicle and the stock infotainment system will go away while the iPhone beams an iOS-style interface to the car screen. From our time with CarPlay, this system appears built from the ground up for computing on the go, with an easy-to-use, safety-focused UI, a heavy emphasis on voice commands, and a sliver of the huge iOS app ecosystem.
To run CarPlay in your vehicle, you'll need a compatible car (Apple has a list here) or an aftermarket radio. Phone-wise, you'll need an iPhone 5/5c or newer. CarPlay updates come up fairly frequently, but this is CarPlay as it exists in iOS 9.2.
The Basics
CarPlay is a "casted" interface—all the processing happens on the iPhone, but it uses the car screen as an external monitor. You plug in the iPhone and tap an icon on the car's stock infotainment system, then the infotainment system goes away and Apple's software commandeers the screen. Audio, touch, and voice commands get beamed to the car, and all the physical controls on the steering wheel and console switch to controlling CarPlay instead of the stock system. It can even invoke Siri by holding down the voice command button. And if the car doesn't have a touchscreen, physical controls are an option, too.