Party Play is a feature available through the NookPhone. Party Play allows you to call your friends and allow for 4 residents to explore the island together.
Players are able to switch out who is the Leader, which is the person doing the main activities (crafting, building, talking with villagers, etc.) The other player(s) will be able to collect items and shake trees, but any items they collect will be put in the recycling bin for players to collect afterwards. (Remember that if you are a follower, and have collected items that you do not want the other players taking, make sure to switch to the leader to collect your items.)