ARKit is an Augmented Reality SDK (software development kit) from Apple for programmers, in particular Camera App coders. The SDK is basically a framework library that helps programmers create Augmented Reality Camera Apps for IOS devices.
ARKit uses Visual Inertial Odometry (VIO) for tracking what the camera sees. It combines the camera sensor data with motion data. And ARKit uses scene understanding to locate horizontal planes for placement of virtual objects onto the scene.
ARKit can also estimate the amount of lighting in a scene to then adjust the brightness for virtual objects to match the scene. It's pretty slick.
This new toolkit is available for use on IOS 11 and is programmed by developers using the new Xcode 9. It's available for both the Swift and Objective-C programming languages.
Some example Apps are already popping up in the App Store taking advantage of this new technology. A pretty good review of these first Apps can be found here on theverge.com
Many more to AR Apps will follow and we will be scouting for the best ones.