The headline feature from today's keynote is that Apple CarPlay will now work via a wireless connection. Currently, for CarPlay to work, a driver's iPhone must be connected to the car's audio system via a USB Lightning cable.
This setup was originally required due to concerns about battery life and the data bandwidth of the Bluetooth protocol. Apple has yet to go into detail about how CarPlay's wireless connection works.
CarPlay will now also support car maker produced apps, which allow the user to control certain aspects of their car without leaving the CarPlay interface.
Other upgrades include the support of higher resolution displays and a greater variety of display ratios.
These new features will be available to iPhone users who upgrade to iOS 9. iOS 9 will be available for developers from today. It then enters public beta in July, with a public rollout planned for late in the third quarter of 2015.
The updated smartphone operating system will be available on all iPhones that support iOS 8. This includes everything from the iPhone 4S and iPhone 5 through to the iPhone 6 and iPhone 6 Plus.
It's not known yet whether existing CarPlay compatible audio headunits will support iOS 9's new feature set, either via a factory-installed upgrade or an over-the-air update.