With iOS 12 you will be able to bring up to four players into the same Augmented Reality (AR) experience on the iPhone and iPad. This allows you to share a game or AR experience with other users. This makes it a group experience instead of something that requires people to look over your shoulder to experience.
In one demo Apple showed a two player AR game where each player uses their iPad or iPhone to control a player and see a shared environment. In this demo a third user watched the players on their own device making it a more immersive and fun experience.
LEGO also showed off a cool new app that uses ARKit 2.0. With this new feature you will be able to play LEGO in AR with up to four friends. You can start with one physical building and then build out a virtual world with players you can control, vehicles to unlock and more. In the demo we saw inside of buildings, a firefighter and a helicopter. When it's time to take a break, the whole thing is saved to the cloud and synced to the set, so you can resume when you have time to play again.