As always, you can battle, live-trade, wonder trade, and use the GTS (global trade system) in OR/AS. You now also have the BuzzNav, a little app on the bottom of your screen that will receive information from people you pass by, and give you little tidbits about what they've been doing in their game. Along with that, people you pass by will have their secret bases loaded into your overworld (for a little while), and their mirage island (a thing you can only reach using the Eon flute, one will naturally spawn every day) will be reachable for that day as well. I may have missed something or another, but I think that's about it! Hope I helped!