Building a multi-user AR experience

The world of multi-user augmented reality has arrived. It's now possible to share augmented experiences through different devices. Google ARCore now has the ability to create these experiences for Android and iOS devices and Apple's ARKit announced this week the ability to share experiences across iPhones.
We'll take a quick look at these new additions to the platforms, then jump in and try and see if we can create an experience in 3 hours or less. How far we make it will be based on who shows up with devices and what people want to try and do. I've got a couple ideas but it will be up to the group to decide. No experience necessary to participate, but if you have experience that would be great!
Bring your laptops, your AR phones/iPads and your thinking caps and we'll see what we can figure out!